Tropical Storm Bill StickNet Deployment Summary

Deployment Preparation

On Sunday, June 14, 2015, a tropical disturbance moved off the Yucatan Peninsula and entered the Southern Gulf of Mexico. Model guidance suggested the disturbance would move into a favorable environment for development and make landfall somewhere along the Southeastern Texas Coast in about 48 hours. Given the run-to-run consistency in the model guidance, preparations for a possible deployment commenced. Beginning around 10:00 AM CDT on June 14, a small team of students including National Wind Institute PhD student and TTUHRT member, James Duncan, Atmospheric Science Group masters student, Phil Ware, and TTUHRT field coordinator, Rich Krupar III, began organizing supplies and tools, checking trailer and truck tire pressures, and charging StickNet external batteries. To the groups surprise, a flat tire was found on the rear drivers side of the new truck used to tow the StickNet trailers. An old rusty screw had punctured through the sidewall of the tire. Immediately, the team took the damaged tire to a local tire shop for replacement. In the meantime, the team traveled to a local hardware store to purchase new bungees, clear silicon, and heavy duty Velcro, to replace old supplies used to secure the StickNet tripods and external batteries, as well as, mitigate water intrusion. Final preparations for the day concluded around 6:00 PM CDT.

Later that evening, Atmospheric Science Group PhD student, Scott Gunter, aspired to deploy three StickNets at the Reese Center airfield, in an effort to satisfy lingering thunderstorm objectives related to his dissertation. With the assistance of myself, both Scott and I deployed three StickNets near the Reese Center mesonet site, in advance of a thunderstorm outflow complex as seen in the panorama shot below.

Outflow winds approaching the Reese Center field site on June 14, 2015. Photo courtesy of Rich Krupar III.

The StickNets remained deployed for several hours as lackluster outflow moved through and dangerous cloud-to-ground lightning illuminated the field site. Around 9:30-10:00 PM CDT, Scott and I retrieved the three StickNet probes and began charging them once again. I left for my apartment immediately after we returned to base to begin packing my bag, in the event that we would pull the trigger and head to the Southeastern Texas Coast in the morning.

Deployment Reasoning

Model runs were monitored overnight for run-to-run consistency and a small meeting took place at Reese to decide on whether or not to deploy, as well as, how many people and StickNet probes would be deployed. The disturbance had not yet been named nor had it gained tropical depression status; however, healthy thunderstorm activity continued to develop around the center of circulation and the upstream environment was still favorable for development. Given limited availability among the TTUHRT, I suggested that the same team that had helped me prepare the previous day go to the Southeastern Texas Coast. Both James and Phil had never deployed StickNet in advance of a tropical system before, so there was a lack of experience to contend with. Also, with limited personnel, only one trailer containing 12 StickNet probes was deployed. The goal of the deployment was to test the refined real-time capabilities of the StickNet probes and make the best possible deployment with a limited window of time. I departed from Reese Center campus at 10:30 AM CDT on June 15, picked up both James and Phil from their home, and we immediately began driving toward the Southeastern Texas Coast.

Deployment Summary

We traveled all day and used Google Earth imagery along the way to scout potential deployment locations. Roughly 3 hours from the target location, we noticed that our diesel exhaust fuel (DEF) was low and had to make a quick pit stop to obtain more DEF. At the same time, we filled up our auxiliary fuel tank, obtained snacks for the long night ahead, and made final checks on our trailer and truck. We began deploying our first StickNet probe east of Angleton, Texas, around 10:30 PM CDT and the National Hurricane Center had just upgraded the tropical disturbance to Tropical Storm Bill. We worked all through the night deploying one StickNet probe at a time on barrier islands, elevated terrain features, and/or in open fields near airports. We deployed our final StickNet probe just before 7:00 AM CDT on June 16 and setup camp in Port Lavaca, Texas, to ride out the landfall of Tropical Storm Bill. A map of all twelve StickNet deployments can be seen below.

Google Earth map of the StickNet deployment (yellow pins) and the National Hurricane Center best-track center fixes (red tropical cyclone symbol).

The team managed to get a few hours of sleep, while members of the TTUHRT back in Lubbock monitored the StickNet real-time data feed. All twelve StickNet probes successfully relayed one-minute barometric pressure and wind summary statistics before, during, and after landfall, demonstrating the capability of the refined real-time telemetry. 

As Bill's center of circulation passed close by the hotel we were staying at, water levels began to rise in Port Lavaca. The combination of the storm and high tide allowed water levels to rise nearly 4 ft. This water level rise led to flash flooding and pier damage in Port Lavaca, as evidenced by the photo I captured in a nearby camper park.

Higher than normal water levels and pier damage at a camper park in Port Lavaca, Texas, on June 16, 2015. Photo courtesy of Rich Krupar III.

The team rested up for the remainder of the day and began retrieving the deployed StickNet probes at sunrise on June 17. The pickup only took 5 hours to complete since there were no obstacles to overcome (e.g. water covered roads). After making a quick lunch stop, the team quickly downloaded the data from each StickNet probe using custom software developed in-house, processed the summary statistics, and began driving back to Lubbock. The team arrived back in Lubbock on June 18 around 2:00 AM CDT.

Overall, given the lack of daylight to scout deployment locations and lack of experience among the team in deploying StickNet in advance of tropical systems, the team achieved its goal of disseminating real-time information during the landfall of Tropical Storm Bill. It was a joy to lead both James and Phil into the field and it made me think back to my first deployment in the North Carolina Outer Banks for Hurricane Irene (2011). I came full circle from the novice to the field leader and it was a deployment I will never forget.

In the next week, I will try and get either James or Phil or both to share their first time experience deploying with the TTUHRT. Stay tuned!

TTUHRT in 2012

Well its been a while... but with Tropical Storm Debby crawling along now is as good a time as any to fill everyone in on our plans for 2012. As Debby was starting to develop in the Southern Gulf of Mexico we commenced our first mass test of all StickNet probes. Every probe was deployed at the TTU Wind Science and Engineering Field site. We use these "mass tests" to ensure all probes are in good working order and to establish what small bias errors may exist in individual sensors as all probes are sampling in general the same environment during these tests.

On the StickNet side of things, we still have our fleet of 24 StickNet probes, 12 of which transmit data in near-real time. Unfortunately, we still have not found funding to upgrade our web infrastructure to provide this information to the general public. The data however is ingested into NOAA Hurricane Research Division's H*Wind windfield model and available to the National Hurricane Center and local Weather Forecast Offices of the National Weather Service. StickNet probes will continue to provide documentation of landfalling hurricane wind fields and will also support research work by TTUHRT field coordinator and Wind Science and Engineering PhD student Rich Krupar. He is examining different techniques to estimate surface wind gust characteristics using WSR-88D radar information. StickNet probes and the good spatial coverage of their observations provide validation. In addition, a probe will be deployed near the closest WSR-88D radar to evaluate Velocity Azimuth Display (VAD) wind retrieval techniques. We will also continue to strive to collect more true marine exposure data as StickNet probes have led to quite a bit more data from the immediate shoreline which is vital in determining how hurricane winds transition from ocean to land.

Big news in the land of the TTUKA radars, each will be getting a new antenna this summer. The upgraded and larger antenna (dish) will allow for even more sensitivity and resolution as we continue to push the frontiers of these mobile radar systems. With this upgrade though it does mean that likely only one radar will be available for hurricane landfall operations during the 2012 season.

And what really matters... advancing our scientific understanding. Dr. Brian Hirth and co-authors (including our Director, Dr. John Schroeder) recently had a journal research paper accepted for publication in the American Meteorological Society's Journal of Weather and Forecasting. This paper focuses on his dissertation research using SMART-Radar data collected during the landfall of Hurricane Frances (2004) to examine how the characteristics of hurricane winds change from the ocean surface to flowing over land mass both in the horizontal and vertical. This is a significant step in understanding how the flow changes and what impacts it may have on how we evaluate coastal building codes. Also myself and co-authors had a paper examining GPS Dropwindsonde and radar derived vertical wind profiles accepted for publication in Weather and Forecasting as well. This work has also helped in determining additional research direction in attempting to use the vertical profile characteristics to forecast expected surface wind gusts.

Well there's a quick update on what we are up to... be sure to follow us on Facebook as we continue to 2012 Atlantic Hurricane Season.

So Long, Farewell, Adios, Au revoir, Arrivederci, Goodbye

Wrote this blog about a month ago and Hurricane Irene interrupted its publication so here it is...

A bittersweet day for TTUHRT as WEMITE 1 and WEMITE 2 towers were officially decomissioned. The two towers were dismantled and their respective trailers scrapped. These two towers were the backbone of our instrumentation fleet for nearly a decade, making over 35 individual deployments for 21 seperate tropical cyclones. WEMITE 1 was also the first ruggedized, self-sustaining, meteorological research tower to be deployed in the path of a landfalling hurricane (Bonnie - 1998). Both towers were mounted and transported on a trailer and collected high resolution data (10Hz) at multiple levels including the official measuring height of 10 m. WEMITE 1 was the doctoral dissertation project of then graduate student John Schroeder, who is now the principal investigator for TTUHRT and the director of the Wind Science and Engineering Research Center at Texas Tech. Data collected from these platforms has appeared in 10 peer-reviewed journal papers, over 25 conference preprints, 9 technical reports, and 6 doctoral dissertations. The records also represent a very large percentage of the complete wind records for a "who's who" list of landfalling hurricanes in the US in the past 13 years. The data collected by these stations also shed light on the characteristics of hurricane winds in an effort to answer our long standing question "is wind, wind?". Recently the database is being applied toward investigating how the turbulence associated with hurricane winds changes with location within the hurricane. The collected information will likely live on for years to come and continue to yield valuable information on hurricanes at landfall.

The towers' final deployment was for Hurricane Rita (2005) and did not participate in the following hurricane seasons of 2006-2010. The platforms have been replaced by the new 2.25 m StickNet probes. The transition to StickNet came about primarily due to the need for greater spatial coverage of hurricane landfalls. With the 2 WEMITE towers plus 3 portable meterological towers, a typical deployment provided 5 observations points. Each tower required at least 1 hour of deployment time for a crew of 4 people. In total, 3 vehicles with at least 6-8 crew members was needed. With the development of StickNet, only 2 vehicles with a total crew of 4 could deploy 24 observing systems, with a deployment time for each probe of less than 10 minutes. The cost/benefit outweighed the lower and "non-official" measurement height. In the climate of rising fuel costs, the reduction of the required number of vehicles also played a large role in the transition. As for the future of StickNet, we hope to expand the fleet to 48 probes using 4 truck/trailer teams.

So this blog was written as a tribute to WEMITE 1 and WEMITE 2. So long and farewell!

Whats New for TTUHRT in 2011

As of the writing of this blog, today marks the "official" start of the 2011 Atlantic Hurricane Season, although tropical cyclones have been documented in every month of the year. TTUHRT has made several improvements to our research platforms during the fall, winter, and spring.

I'll start first with our StickNet platforms... for those that don't know, StickNet probes are rapidly deployable 2.25 m weather stations. They make research grade measurements of wind speed, direction, temperature, barometric pressure, and relative humidity. Our group was awarded a grant in 2010 from the Texas Applied Research Program to equip 12 probes with real-time data transmission capability. 12 probes were upgraded with cell internet capability to transmit data in real-time to our servers at Texas Tech. During operations, data will be available to the National Weather Service, National Hurricane Center, emergency management, and our private research partners. Additionally, NOAA's Hurricane Research Center will ingest the observations into their H*Wind surface windfield model. Unfortunately, the data will not be directly available to the general public. Our web server capability likely would not handle the amount of traffic during a landfalling hurricane. Also we are still ironing out the information that will be transmitted as well as the quality control and assurance procedures. We hope in the coming years to be able to provide this information to the general public through upgrades to our server infrastructure. As in the past, summary data will be posted to our official website as soon as possible following any deployment operations. The same 12 probes also received new data acquisition enclosures and new ruggedized instrument connectors. This retrofit was conducted to make the platforms even more rugged and limit any water intrusion into sensitive electronic components inside the data acquisition enclosure.

The other major improvements were focused on the TTUKA mobile Doppler radars. Each radar received a new and improved data processor. The new processor (RVP 9) will allow for even higher resolution information to be collected. A good analogy is if we are looking at a row of fence posts, with the old system 2 fence posts were identified as 1 return, with the new processor we can distinguish each fence post. The radar now has a radial resolution of approximately 5 m with an azimuthal resolution of 0.5 degrees. The upgrades increase our capability to observe small scale turbulent features.

Stay tuned to the blog as our new field coordinator Rich Krupar will cover these upgrades in greater detail. We are very excited about our ability to continue to make critical measurements of hurricanes at landfall... with the end goal of "making landfalling hurricanes more like a bump in the road to society"

Anatomy of TTUHRT Landfall Operations

Well as we head into October the tropics have quieted down a bit. TS Matthew dissipated over central America while short-lived TS Nicole and its remnants are helping to produce prolific rainfall totals across the east coast of the US.

I thought I would take a blog and discuss just how a TTUHRT deployment for a landfalling hurricane actually works. Since Lubbock is a long way from the coast, logistical concerns are pretty significant. How do we get 24 StickNets and 2 mobile Doppler radars to the coastline, amidst evacuation traffic, get probes deployed and collecting data, find suitable radar sites that are unobstructed, and then retrieve all of our instruments.

We will start first with just deciding if or when to depart... We monitor the tropics pretty closely especially during times when active cyclones are present and even provide forecast discussion emails within the university, to our private funding sources, and our government and university partners. These provide information regarding the current large-scale weather pattern that may influence the hurricane, track guidance from computer models, and the forecast of what the hurricane and the environment may look like in several days. Over the past several years we have developed a loose set of criteria to help us determine if we should conduct landfall operations. These are based in part on science objectives as well as our current level of funding and logistical concerns. An example would be, a weak Saffir-Simpson category 1 hurricane along the east coast of Florida. In this situation, a trip to this area of Florida is quite expensive given the cost of fuel, hotel. and per diem expenses for the crews. For the sake of this example, we will say we have no specific science objectives other than monitoring and documenting the hurricane wind field. Well for this situation, we already have a large database from lower end hurricanes as they are the most common. We would likely decide not to deploy for this storm. However, if there was a specific science objective, we would deploy. An example would be using the Ka-band radar systems to examine the interface of the eye/eyewall. For a very strong hurricane, this experiment would likely be too dangerous to employ, but for a weaker storm that we do not have wind load concerns on the radars, we could execute this objective and obtain a quality dataset. Also funding, as is the case with most scientific field studies, controls how many deployments we can make. Unfortunately, we do not have an unlimited budget and must balance the cost/scientific reward for each deployment.

Now lets assume we have an established Saffir-Simpson category 2 (peak 1-minute average winds of 96-110 mph) "Hurricane Ian" entering the southern Gulf of Mexico. The forecast environmental conditions are expected to be favorable for strengthening with low wind shear and the storm is likely to pass over a swath of very deep and warm water associated with the loop current. All signs point to an intensifying hurricane with the forecast tracks in good agreement on a landfall along the northern Gulf coast, like those shown to the left from Hurricane Gustav (2008). In our hypothetical situation, landfall of our system would be near 180 hours or 5 days out. It takes us approximately 12-15 hours to reach most of the northern Gulf coast. For StickNet operations we usually like to use a whole day to scout deployment sites along the coast. This also gives us a chance to investigate how close we can get probes to the immediate shoreline. We also require approximately 12 hours to complete a full StickNet deployment. For safety concerns, we try to complete the deployment prior to the onset of 50 mph wind speeds. In these sustained wind conditions, damage typically begins to occur especially to tree limbs. This allows us to begin our deployments approximately in teh 24-36 hour window prior to landfall. The timeline requires a departure from Lubbock often several days in advance of the hurricane. Once again for safety, we try very hard to avoid having to drive through the night to reach our target. However, in some instances such as Hurricane Charley (2004) which intensified very quickly, it requires driving straight from Lubbock to the target area. For Hurricane Charley, this meant driving 23 hours straight to Sarasota, FL.

On to the actual deployment... We have our target area defined for "Hurricane Ian" of the upper-Texas coast and we feel that this will meet deployment criteria, so it is time to hit the road. The StickNet crews are broken into two teams of two people. Each team is responsible for deploying 12 probes which are housed in a covered trailer. We use Dodge 4x4 diesel trucks to pull the trailers. The trucks are outfitted with cell Internet routers to allow us to monitor the storm while in transit and to use Google Earth aerial imagery to locate possible deployment sites. For each of the two Ka-band Doppler radars, we also have two people manning each. The radars are also equipped with mobile Internet. As we arrive in the area, navigating through evacuation traffic can be difficult. We often try to use roadways not specifically assigned as evacuation routes. Assuming there is time, both the StickNet and Ka radar teams will scout for potential deployment sites. For StickNets, we are looking for open exposure areas which are free from obstacles in most directions. The more obstacles means the larger frictional force to slow the wind speeds and afterall we are trying to measure the strongest winds. In the past with the larger WEMITE towers, airports have provided good deployment sites. With the versatility of StickNet, these sites have been used less. If we do use an airport or park site, the field coordinator (which has been me since 2005, although Rich Krupar will take over in 2011) will obtain the necessary permissions to allow for the probe to be deployed. The Ka-radar teams are also searching for sites which are unobstructed, as buildings and trees can block the radar beam. After a day of scouting and marking deployment sites the teams try to get a good night's rest before the action gets going the following day.

Showtime...Now we are getting to the business of making a full deployment as "Hurricane Ian" is now only 36 hours from landfall along the upper-Texas coast. Usually by this time the spread in computer model tracks has become much smaller and we can really get down to figuring out exactly where the hurricane is going to come ashore. We also evaluate the structure of the wind field as often we are targeting the area of strongest winds. Most of us know that the strongest winds in a hurricane are within the eyewall in the right-front quadrant of the storm. This is the location where the wind is aligned with the direction of motion and the flow of air is on-shore. Water surfaces are much smoother than land, thus the wind speeds are not reduced as much due to surface friction, unlike in the off-shore side where air traverses across the land. We often use a tool called H*Wind to evaluate the general wind structure of the hurricane. H*Wind was developed by Dr. Mark Powell at NOAA's Hurricane Research Division. It is a wind field model that uses observations from all types of instruments (aircraft, dropsondes, satellite wind estimates, ASOS stations, Ship reports etc... etc...) to synthesize a near real-time picture of the hurricane's wind field. An example analysis is shown on the image to the left from Hurricane Ike (2008). This allows us to target the region where we expect the maximum winds to come ashore. In the case of Hurricane Ike, we decided to concentrate most of our probes within the wind maximum in an attempt to make fine-scale measurement across this region (shown in the image to the right, H*wind maximum wind swath and TTUHRT probe locations). This allowed us to evaluate the local variability in the wind field as probes were spaced approximately 8 miles apart. As we have found, each deployment has differences and never goes exactly according to plan. We must account for storm surge issues and road networks. A good example is from Hurricane Gustav where the Atchafalaya swamp kept us from having a continuous array of probes across the landfall region.

As for the Ka-band radar deployments we have yet to have an opportunity to deploy both systems. Ka-1 made its first venture into a tropical cyclone during Tropical Storm Ida last year. The primary deployment strategy we would like to use is a dual-Doppler one. The use of two radars allows for the complete 3-dimensional wind field to be derived through some higher order math. One Doppler system can only sense 1 component of the wind (toward or away from the radar). With the proper orientation, 2 radars can get the total wind speed and direction fields. Given the wavelength of our radars, this requires the two radars to be located fairly close to each other (maybe only a couple miles apart at the most). Possibly even at the opposite ends of the same airfield. Another strategy involves single Doppler sampling of the eye/eyewall interface to examine mesovorticies within the eyewall. I'll let Pat Skinner and Scott Gunter go into some more detail regarding radar sampling strategies in some later blogs. In case you were wondering, our radar systems were designed to withstand sustained windspeeds near 120 mph. This is the main reason we have a complete radome over the antenna in order to reduce the wind loads on the antenna itself. This allows the system to be deployed in higher windspeed environments. All contingent on the lack of flying debris which is one of the most dangerous aspects of a landfalling hurricane.

After the deployment we find a safe hotel, typically not in the direct path of the eyewall. However, we do try to remain close to the array as it makes retrieval much easier. Often law-enforcement closes the impacted area to outside traffic, so remaining close by allows us to avoid this issue. This often means staying in a hotel with no power. We try to stock up on snack food and water prior to landfall and fill up the bathtub with water as anyone should do who is planning on riding out a hurricane. This sometimes means a diet of poweraid and potato chips for a couple days. After all the StickNet probes have been deployed, the teams retreat to a hotel to ride out the storm. In the case of the radar crews, their job is just beginning. A radar operator is required to be in each radar through the event to ensure the system is operating correctly with no problems. The ideal situation allows the StickNet crews to be nearby to shuttle radar personnel back and forth between the radar and the team's hotel. Unfortunately if conditions become too hazardous for relief crews to be shuttled in, the radar operators may be required to work for significant lengths of time. Once the storm has passed or data collection has been called off, the radar teams can un-deploy and depart the area. The StickNet teams however must retrieve their respective probes. This can go smoothly as in the case of Hurricane Gustav or can be quite difficult such as following Hurricanes Dolly and Ike. Downed power lines can cutoff areas as well as storm surge and freshwater flooding. In fact, Probe 110A stayed at Ft. Travis on the Bolivar peninsula for 3 weeks after Hurricane Ike (image to the left), as the area was only accessible by boat. It was eventually retrieved by personnel from the Galveston County Emergency Operations Center, and we are indebted to them for their help.

Data collection and dissemination...Following the retrieval of all of the StickNet probes, each data acquisition box is plugged into an Ethernet hub in each trailer. Data is downloaded and summary statistics are computed through a computer program. This allows TTUHRT to disseminate data summaries to pertinent agencies as well as our private funding institutions. We typically are able to distribute deployment information which includes deployment maps, site summaries, and data statistics within 12 hours of retrieval. The data collected from the Doppler radar systems takes much longer to analyze and initial plots will likely take several days following the team's return to Lubbock and Texas Tech. Once the team returns to Lubbock, products are created for display via our website. These include the summary statistics, deployment maps, and data plots for each probe.

As for the science objectives, the collected data eventually makes its way into M.S. Theses and Ph.D. dissertations, scientific journal articles, and technical reports. This process takes a significant amount of time and often results take years to produce. In later blogs, TTUHRT scientists will talk a little about their individual research topics.

Tropical Depression #15

Tropical depression #15 has developed this afternoon in the south-central Caribbean as shown on the visible satellite image on the left. The depression has become more organized as thunderstorm activity continues to increase near the center of circulation. The future of the depression in the long-term is quite unknown at this time. The system is forecast by most of the computer models to continue westward, possibly clipping the coast of Nicaragua or Honduras before heading toward the Yucatan peninsula. At this time is when the forecast gets muddy. Most of the models indicate that the cyclone may reach a region of weak steering near the Yucatan. Quite a bit hinges on if the system makes landfall on the peninsula or remains offshore. IF the system remains offshore it has a greater potential to be a significant storm later down the road. The official forecast from the National Hurricane Center does call for the depression to become a hurricane prior to reaching the Yucatan peninsula. Right now most of the computer representations of the atmosphere are struggling to figure out where this storm may go after reaching the Yucatan, due in part to an upper-level low which may get stuck over the southeastern United States. There is some that suggest that the low may be able to turn the cyclone northward into the Gulf of Mexico. It is too early to tell right now but we will monitor this storm closely as it may represent the highest threat to the US since Hurricane Earl several weeks ago.

2010 Atlantic Hurricane Season... So far

I'd like to take a blog to discuss a little about the 2010 Atlantic hurricane season to date. Prior to the start of the season, the majority of the agencies, universities, and private groups that provide seasonal forecasts suggested that the 2010 season would see above normal activity. This was not a surprise given that ocean temperatures across the Atlantic basin were and still are significantly above normal and we were entering a La Nina phase in the equatorial Pacific which typically enhances tropical cyclone activity in the Atlantic basin. Although seasonal forecasts from NOAA and Colorado State University have shown some reasonable skill at predicting overall activity, currently there is no skill in determining if a season will feature more landfalls along the US coastline or not.

2010 got off to a quick start with Hurricane Alex, shown making landfall in the radar image to the left. This storm made landfall only a 130 miles south of the Texas/Mexico border as an intensifying category 2 hurricane at approximately 02 UTC on the 1st of July. Alex featured a very low central pressure of 946 mb, which is often supportive of a stronger hurricane, but the wind field had not responded yet and had the system had another 12-24 hours over water it would have likely been a major hurricane. In any event, Alex was the second strongest June hurricane on record. Fortunately for the residents along the lower Texas coast a strong ridge of high pressure over the Gulf of Mexico kept Alex from making landfall further north.

Despite the quick start, the season slowed considerably with short lived storms: Bonnie and Colin. Although the tropical wave activity continued to roll off the African continent, waves had to deal with a variety of inhibiting factors. The most dominant was a very dry eastern Atlantic due in part to a significant amount of African dust, known as the Saharan Air Layer (SAL). Several recent scientific papers have focused on the SAL as both an inhibiting factor and a feature which can aid in tropical development. In this case, the SAL appeared to inhibit development by providing a very dry and stable airmass across much of the main development region. Coupled with the SAL is an easterly jet feature which is often present in the middle layers of the troposphere across the eastern Atlantic. This can induce wind shear on a developing tropical cyclone, thus not allowing the system to organize. Also the presence of a parade of upper-level low pressure areas across much of the central Atlantic increased the wind shear levels as well. All of this contributed to a relative lull in the tropical activity from July through mid August.

Activity quickly picked up as Hurricane Danielle developed. I have stated this before but it seem as if the atmosphere switched the tropical cyclone genesis switch into the "on" position. What would ensue was a parade of tropical cyclones most of which developed from tropical waves emerging off the western coast of Africa. These systems are often referred to as Cape Verde's due to the development region's proximity to the Cape Verde Islands. Many of the major hurricanes in our historical record were of the Cape Verde variety. Danielle would go on to become the first "major" hurricane (cat 3 or higher) of the 2010 season but recurve harmlessly out into the north Atlantic. Danielle was followed by Earl (image below) which made a much closer approach to the US before finally making landfall as a tropical storm in Nova Scotia. Earl, like Danielle, intensified to a major hurricane just after passing near Anegada in the northern Leeward Islands. Earl would eventually pass approximately 100 miles east of Cape Hatteras and the outer banks of North Carolina. Up next were short-lived tropical storms Fiona and Gaston.

Up next was Hermine, a storm that rapidly intensified from a tropical depression to a strong tropical storm in 21 hours in the Bay of Campeche. Hermine came right up to the brink of being classified a hurricane at landfall in Mexico, well south of the Texas/Mexico border. Hermine however reminded us of the threats that even tropical storms can pose as the system proceeded northward after landfall into central Texas. Hermine dumped nearly 10 inches of rainfall across the Austin, TX metro area and rainband convection spawned several tornadoes in the DFW metroplex. Tornadoes associated with tropical systems are typically found in the rainband regions and can occur well after landfall. In fact, one of our graduate students and TTUHRT blogger Scott Gunter is currently analyzing data collected from the SMART-radars during the landfall of Hurricane Frances (2004). His dataset focuses on two individual cells within an outer rainband of Frances that contained rotational signatures.

Moving on in the 2010 Atlantic season brings us to Hurricane Igor, Hurricane Julia, and Tropical Storm Karl which were all active at the time this was written. Igor (image to the right) and Julia both developed from vigorous tropical waves almost as soon as they exited the African coast. Both also went through significant phases of rapid intensification. Whereas Karl developed in the western Caribbean, making landfall as a Tropical Storm near the Belize/Mexico border. Igor and Julia are both forecast to turn northward into the open Atlantic and will likely not threaten the east coast of the United States. Although Igor may be a potential threat to Bermuda. At the time this blog was being written, both Igor and Julia were category 4 hurricanes. The last time two category 4 hurricanes were active in the Atlantic basin was in 1926.

Looking back, most of our Cape Verde systems over the past month have fortunately followed a similar track and recurved out into the open Atlantic and have not been significant threats to the United States. Why is this? well hurricanes are steered by the flow of air over a large depth of the troposphere. They typically move around large and deep areas of high pressure (ridge). Well typically during the peak of the hurricane season a well established ridge is present over the central Atlantic, known as the Bermuda-Azores High. Often tropical systems follow the southern extent of the ridge westward as this is the "path of least resistance". If the ridge does not extent far enough westward the system will simply rotate around the ridge and move more northward. This has been the case this season, as a series of upper-level low pressure areas or troughs have passed through the flow and weaken or erode the western side of the Bermuda High, thus allowing tropical systems to follow the "easy" path northward around the ridge. In 2004 and 2005 this was a different story as the ridge extended far enough westward to simply push systems toward the continental United States. Although this is a very simplistic representation of the steering regimes of tropical cyclones it gives a general idea how Cape Verde storms often progress. Predicting this pattern prior to the season is quite difficult, thus estimating the risk to areas of coastline before the start of a hurricane season is a tremendous forecasting challenge. As far as activity for this season, despite the slow start it is well on its way to being a very active year. So far this season has featured 11 named storms, 5 hurricanes, and 4 major hurricanes (Danielle, Earl, Igor, and Julia), an average season has 10-6-2. So with about 45% of the season remaining it looks like the seasonal forecasts of an active year will verify.

In the next blog, I'd like to highlight a little about the ongoing research within our group here at Texas Tech.