Saturday, September 18, 2010

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 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


Monday, August 16, 2010

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

Sunday, August 15, 2010

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.

Tuesday, July 6, 2010

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.

Friday, July 2, 2010

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

Wednesday, June 30, 2010

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