West Caribbean/Gulf Heating up over the next few weeks

The tropics over the past week have certainly lived up to the statistical expectations as we head past the peak of the 2010 hurricane season. So far this part of the state has seen just the outer most affects from several tropical storms and hurricanes that have entered the western Gulf the past few months, giving the region some much needed rainfall and break from what has been a very hot summer.

The upper level steering flow thus far in the season has thankfully kept such storms as hurricane Alex, tropical storm Hermine, and Hurricane Karl, south of the border, all making landfall in northern Mexico. However, long range computer models have been hinting that things might really start to ramp up across the western Caribbean sea later in the week...an area that has seen very little tropical activity so far and is therefore a prime region for rapid development should a system develop locally or move into that area.

An indice that hurricane forecasters monitor closely throughout the season is called the MJO or Madden-Julian Oscillation. It tracks the 30-60 day fluctuation of rising and sinking air, most notable across the Indian and Western Pacific oceans. The two scientists found that there was a pulse of increased thunderstorm development and tropical cyclone development that begins in the Indian Ocean and then moves east across Indonesia, into the western Pacific, central Pacific, and then into the eastern Pacific ocean. What was also found out is that about 8-10 days after the MJO reaches the eastern Pacific, there was a significant increase in tropical development across the Gulf of Mexico and Caribbean sea.

The latest projections indicate that we will be seeing a MJO pulse moving into the eastern Pacific which will likely be a positive factor, helping to increase the potential for development across the western Caribbean over the next week or so. This pattern looks to be getting picked up by the global models as well as they are now forecasting the development of a tropical system in the western Caribbean sea late next weekend and early next week (9/26 through 9/28) depending on which model you are looking at. Right now, since it is so far out in the future, it would be pointless to try and determine where such a system might go but the consistency among the models is a good indication that we will likely see activity start to ramp up as we head into the latter part of September and first week of October.

12z GFS Model









12z ECMWF

Afternoon storms and the remnants of TD 5 weaken

Broken line of showers and thunderstorms that developed along a strong outflow boundary (many locations across the city saw 30-40mph winds as it passed by) from storms over LA is now well southwest of the metro-Houston area and will likely continue for the next couple of hours. Much cooler temps in the upper 70's and lower 80s along with some stratiform rain, associated with a meso-high that has developed in the wake of the storms, is all the remains across the city. Another impulse can be seen generating scattered convection over LA moving southwest; however I think that the atmosphere will be to stable to support its continuation much past sunset. We will have to keep an eye on any outflow boundaries which maybe located across the region for a possible focus for thunderstorm development tomorrow afternoon.

Conditions will remain favorable for at least scattered afternoon and evening shower and thunderstorm activity as we see deep moisture remain in place...being pulled around the western side of the remnant low from TD 5.

The remnants of TD 5 are showing much less organization this evening with the low level center becoming completely exposed to the northeast of the convection. The latest surface maps also shows the pressure gradient at the surface might be weakening, as seen with some westerly winds being noted north of the center (opposed to easterly winds which would be expected from a stronger closed low). It might try and re-form a center under some of the convection seen south of the Mississippi coast over the next 12-20 hours or so, however it is quickly running out of time to do much as it continues off to the west. With the system having not strengthened much today, am still not expecting very much in the way of an impact to our local weather other then to keep moisture levels high, and bring the occasional disturbance across the area helping develop local showers and thunderstorms.

KHGX radar image with meso-high and outflow denoted:

Wind Speeds showing passing of outflow at UHMT:

Satellite and surface obs showing the weakening pressure gradient (The circled winds were being influenced by the system earlier today...not any more):


18z Model Guidance on remnant's of TD 5:

Weak front and remnants of TD 5 organize in northern Gulf

Latest surface analysis this morning indicates a very weak frontal boundary (more like a wind shift line) is currently located across north Texas between Dallas and Waco. It is looking like the Texas end of the boundary is pulling up stationary and will likely start to wash out later this afternoon and evening. Surface winds across southeast Texas are out of the west and northwest in agreement with the GFS model which indicates that we will continue to see winds veer around to the northeast and east by late afternoon.

Morning and model soundings show that the atmosphere across the region is extremely moist and unstable with precip water values in the 2.2 - 2.3'' range, a K-index around 40 (numbers above 30 would tend to indicate scattered to numerous convection), and convective temps in the lower 90s. The only fly in the ointment for some cooling rain would be some capping indicated in the GFS model soundings for this afternoon. The isolated showers that developed earlier this morning across Montgomery county and eastern Harris county look to have been associated with an outflow boundary from convection in Louisiana. I would expect at least some scattered shower and thunderstorm activity around the area this afternoon as temps warm into the lower to mid 90s. Soundings do indicate a slight chance for some strong winds under the stronger storms that can manage to develop.

Of greater interest is the remnant low from TD 5 which is now out over open water south of the Pensacola, FL/Mobile, Al area. The latest tropical weather outlook from NHC gives the system a 60 percent chance of development over the next 48 hours or so. At this time the 00z hurricane models show the system moving into southern or southeastern Louisiana around the middle of the week. Morning visible satellite imagery shows some possible banding features taking shape to the north of the center of circulation...possibly an indication that the low will start trying to wrap up over the next few hours or so. A hurricane hunter aircraft is currently scheduled to investigate the system this afternoon. Should something develop today, look for an update to the blog. At this time it looks like effects on our local weather from this low will be minimal, however that could change quickly with just a small adjustment in the track westward so this will be something to watch very closely over the next day or so.

Surface map showing gulf Low, Satellite imagery, and 12z Model Tracks

Weak Front and Remnants of TD 5

It looks like an interesting first half of the week across southeast Texas as several features could potentially impact the region. The first feature to watch will be a weak frontal boundary currently (1pm Sunday) located across northern Oklahoma which is moving south. The second will be the remnant low of TD 5 that is spinning across southwest Georgia; currently forecast to possibly move south into the north central Gulf and run about a 30 percent chance for tropical cyclone development over the next 48 hours. Both of the systems will likely play an important roll and tend to complicate in our wind forecast the next few days.

Wind direction will be the main challenge....if the weak front can make it as far south as the Houston area, we will likely see more northeasterly and potentially easterly winds; however, as we will be on the western side of the low forecast to slowly develop over the northern Gulf, our winds may turn more north-northwesterly, to possibly westerly depending on the future track and strength of the low. A stronger low and more westerly track would give us a much more northwesterly wind flow....a weaker low and a further easterly track might not have much influence on our local winds at all, keeping them more northeast should the front make it down here.

The 12z models have some timing differences but do generally agree in bringing northerly winds, changing to northeast then east-southeast through the day Monday across the Houston area. The NAM shows southwesterly winds during the morning turning north-northwesterly towards noon then back around to the southeast by the late afternoon and evening. The GFS keeps weak northwesterly winds across the region during the morning turning northeast to east by the afternoon. Therefore it looks like the best window for easterly winds will be 18-00z Monday. Otherwise we will likely see northerly winds during the day which could bring down pollution from the Dallas area. All in all, it looks like an interest few days.

12z Forecasting Sounding for Hobby Airport showing how winds change during the day.

Two tropical systems...heavy rain threat through Friday

Here we go again....we are currently watching two tropical systems that will have an impact on southeast Texas this week. The first is a well defined tropical low that moved inland across south-central Louisiana yesterday, producing flash flooding and is moving toward southeast Texas; the other is a strong tropical wave over the Yucatan peninsula that is forecast to head toward the lower to middle Texas coast by Thursday. All in all, these two systems will once again bring in some very deep tropical moisture out of the gulf and give us another threat for heavy rain.

LA System:
The small area of low pressure that moved inland in south-central LA yesterday is now located to the northeast of the Lake Charles area and is starting to take on more semi-tropical characteristics. As this low moves west, very deep tropical moisture, marked by precip water values in the 2.4-2.6'' range will spread into southeast Texas from east to west this afternoon and evening. Current thinking is that we will see scattered shower and thunderstorm activity on the west side of the low this afternoon before things transition over to more of a nocturne core rain event overnight tonight. Right now, it looks as if areas east of I-45 will have the greatest likelihood of seeing these core rains. Tomorrow, the surface low will be off to the northwest of the region allowing for a deep moisture tap to setup across the area. Expect widespread showers and thunderstorms to develop with heavy rain. With the moist ground conditions, the flooding threat will be high, especially in areas of poor drainage.

Invest 96L currently impacting the Yucatan peninsula and is forecast to move off into the southern Gulf of Mexico over the next 24 hours. At this time the system is not showing any signs of significant organization in the shower and thunderstorm activity and therefore the NHC has given the system about a 30 percent chance of development. The latest models have backed down on trying to develop a well defined low with the system, although upper level winds will be favorable for the development so this will need to be watched closely over the next few days. Will be watching for several scenarios to possibly play out as far as the rainfall threat is concerned. Models indicate that the tropical wave, or possible surface reflection should reach the middle-Texas coast Thursday with a significant amount of moisture advection on the northeast side of the system. Therefore, they really hammer the middle to upper Texas coast and southeast Texas with a significant amount rain late Wednesday and Thursday. If the system manages to close off into a low, then the heaviest rains could be focused closer to where the center crosses the coastline...which would be more toward the middle-lower Texas coast. Needless to say, there is still a good bit of uncertainty as to how this system will impact the region; therefore it will be important to monitor the latest forecasts over the next few days concerning the development of the system.

Look for additional updates throughout the week concerning the tropical and heavy rainfall threats to the region.

Heavy Rain Threat Continues

Heavy rain has plagued portions of southeast Texas since the landfall of Hurricane Alex two days ago. Very deep tropical moisture remains in place across the region with extremely high precip water values in the 2.6-2.8'' range. The boundary that plagued western Brazoria and Matagorday counties yesterday dropping 6-10'' of rain is slowly starting to move inland and is edging closer to metro Houston this morning. Scattered showers and thunderstorms continue to develop along this boundary and move northwest. We are going to have to keep a very close eye on the training situation today as the boundary moves into the city as flash flooding could become a problem. Heavy rain will remain the main weather threat into tomorrow across southeast Texas.

Storm Total Precip through 6:30am

Alex approaching the coast

At 4:00 PM CDT, Hurricane Alex was located near 24.4N/96.8W, or about 105 miles southeast of Brownsville, Texas and about 50 miles east of the coast of Mexico. Maximum sustained winds are near 90 mph. Alex has been moving to the west around 12mph. After taking a jog towards the north-northwest this afternoon it looks like the upper level ridge is now influencing the cyclone and Alex is expected to continue moving west until landfall which could be in the next couple of hours.

Alex continues to have a very organized appearance on the latest high res visible sat imagery with a very well defined but small eye emerging as he nears the coast. Surface pressure has dropped once again and is currently at 959mb so it looks like Alex is really trying to complete the eye-wall replacement cycle which began late this morning. Latest radar data shows that the cyclone is once again developing a well defined inner eye which could mean that it is just about finished with the replacement cycle and a further increase in surface wind speeds are possible before landfall. Alex remains a very large storm with tropical storm force winds extending out up to 200 miles from the center. It looks like however, that the sustained hurricane force winds should remain south of the Brownsville area.

Local radars continue to show showers moving inland from the gulf as deep tropical moisture remains in place across the area. Rain chances will remain high through the weekend and even deeper moisture arrives later tonight. Locally heavy rainfall will remain the main threat; however there could be a very isolated tornado in any of the heavier convective bands that might develop and push onshore. Widespread 1-2 inches of rain with isolated 2-4 inches seem like a good bet through Friday evening.

KBRO Radar


KBRO Storm Total Precip

Alex North of Track

The latest satellite imagery shows that Alex is currently traveling to the north of the 10am NHC track forecast. This could be because the upper level ridge that computer models have been forecasting to start pushing the cyclone off to the west has been slower to build across the northern gulf coast. The storm does look like it could be starting to make that more west-northwest turn based on some of the latest radar data; however the storm is going to still be north of the current track. It would not surprise me to see the NHC adjust their 1pm track a bit further north up the coast.

Satellite and Track Overlay

Alex Continues to Strengthen

At 10:00 AM CDT, Hurricane Alex was located near 23.9N/95.4W, or about 185 miles southeast of Brownsville, Texas. Maximum sustained winds are near 80 mph. Alex has been moving to the northwest near 5 mph. Latest high resolution visible satellite imagery shows that Alex has been tracking north (or to the right) of the latest NHC track, likely in response to a continued upper level weakness to the north of the cyclone. Current thinking is that this weakness should start to be replaced by a ridge over the next few hours. As this occurs we should see the system resume more of a west-northwest track and head inland tomorrow morning in northern Mexico.

Alex has quite an impressive presentation on the latest satellite images which show a very well organized storm this morning with improved upper level outflow. The latest data from the Hurricane hunter aircraft indicate that the cyclone is currently going through an eye-wall replacement cycle and that the inner eye-wall has collapsed and the pressure has risen to 961mb, up 2mb from earlier this morning. The atmosphere around Alex is very moist to dry air entrainment does not look like it is going to be a limiting factor for increased strengthening today. Much like we saw with Ike, the storms central pressure is already that of a category 3 storm; however the storm is so large that the wind field will take some time to catch up with the pressures. I do not think that the storm will have enough time to fully complete its eye-wall replacement cycle and allow for the development of another strong inner eye-wall before landfall. Therefore it still looks like Alex will be a cat 2 hurricane with max sustained winds around 100-105mph as the storm reaches the coastline.

The main threats for southeast Texas will be the potential locally heavy rainfall due to a very tropical air mass in place over the region. Precip water values this morning are running in the 2.5-2.6'' range which is easily 2 standard deviations above normal for this time of year, meaning that any of the heavier convection will be capable of putting down 2-3'' per hour rainfall rates or greater. This will likely lead to some street flooding problems should we see training setup over the metro area. As of 11am, most of the activity has been confined to our coastal counties and offshore which is where the greatest risk of flooding should remain for the day. We will need to keep a close eye on the radar however to see if the heavier activity that has been over the gulf starts to move inland.

Winds across the region should remain out of the east-northeast 15-20mph through the day with some gusts to 30mph, especially in the heavier storms.

Alex Satellite Imagery

10am NHC Track

Models shift back south

Discussion..

Well, the 18z suite of models has resulted in a major shift in the three models (GFS, CMC, and GFDL) that seemed to be the northern outliers but really got forecasters attention over the past couple of days. Now all of the major dynamic models with the exception of the HWRF are now predicting a landfall right around where the 4pm NHC track is currently positioned about 100 miles south of Brownsville, TX. It seems like as Alex has now moved into the gulf, the models are able to ingest better data and initialize better and have seemed to come into pretty good agreement with a ridge of high pressure forecast to build to the north of the storm and turn it more west-northwest, towards northern Mexico. It is still very possible due to the slow forward speed, that Alex could still move to the right of the current forecast and impact south Texas. Tomorrow is looking like the pivotal day in the track forecast because that is when Alex is currently forecast to make that more westward turn in response to the building ridge to its north-northeast. If that does not happen, then Alex could take more of a northerly track and head more towards the middle Texas coast.

Houston Impacts..

With the center of Alex currently forecast to remain well south of the area really strong winds do not look like an issue; however very deep tropical moisture with precip water values around 2 standard deviations above normal will continue to move into the region for the remainder of the week. This will likely produce periods of heavy showers and thunderstorms and the possibility of some localized flooding problems. The latest 5-day rainfall total forecast from HPC (Hydrometeorological Prediction Center) shows the potential for a widespread 1-3 inches with isolated 3-6 in totals if we see training setup. Depending on the future track of Alex, some outer rain bands may begin to affect areas south of I-10 as early as Wednesday afternoon or evening. Isolated tornadoes and gusty winds up to 40mph could be possible if we see some of the stronger squalls reach the coast later this week; however this will be highly dependent on the future track of Alex.

At this time I would expect to see winds at UH turn more east to northeast Wednesday and Thursday and increase into the 15-20mph range with gusts 25-30mph.

For UHCC, look for east winds increasing to the 20-25mph range with gusts 30-35mph Wednesday and Thursday.

4pm NHC Track


18z Tropical Models

TS Alex Possible Texas Threat?

Since the last time the blog was updated was for the approach of Hurricane Ike back in 2008, the potential threat from Alex seems to be a good place to start up again.

The first tropical cyclone of the 2010 season is presenting forecasters with anything but an easy forecast. As of 10pm Alex has re-emerged into the southern gulf and is centered at 19.4N/91.3W, or about 470 miles east-southeast of Tampico, MX. Maximum sustained winds are near 45 mph. Movement is to the west-northwest at 7 mph.

The forecast track over the next 36 hours or so looks pretty good with Alex expected to continue to generally move off to the northwest; however as we get into day 3 and beyond there remains a great amount of uncertainly in regards to the future track Alex will take. At this time the storm is expected to begin to interact with a ridge of high pressure forecast to be located across the northern Gulf of Mexico. The main question remains how strong the ridge across the northern gulf will be as we see a trough of low pressure drive south across the eastern US. A weaker ridge will allow for Alex to turn more to the northwest and north and head toward the middle to upper Texas coast. A stronger ridge, which the NHC forecast is currently based on will turn Alex more toward the west-northwest and then west into the northern Mexican coast about 150 miles south of Brownsville.

This uncertainty is reflected in the dynamic models, four of which (GFS, GFDL, HWRF, and CMC) calling for a Texas landfall while the NOGAPS and ECMWF take the storm into northern Mexico. Interestingly enough, the best preforming models at the 3-4 day range last season were the GFS and the CMC (Canadian) with these models forecasting a middle to upper Texas coast landfall Thursday or Friday of this week. The current NHC track is slightly further north but still takes Alex into the northern Mexican coastline; however, another item to consider is the right bias associated with land-falling gulf storms. It would not surprise me if we see the NHC continue a northward adjustment to future tracks if the dynamics models start to trend closer to the GFS and CMC which at this time remain the northern outliers.

Therefore having said all this, it would be a safe bet to start looking over your hurricane preparedness plans just to be on the safe side.

Below is the current NHC forecast track along with the 00z dynamic models and a link to Dr. Jeff Masters blog on Alex which is a very interesting read and has some more statistics regarding which models preformed the best last year.

10pm NHC Track


00z Models


http://www.wunderground.com/blog/JeffMasters/article.html