SE TX/SW LA weather: Much cooler and WET after Tuesday

[srainhoutx]

HGX thoughts this afternoon...

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
250 PM CST WED NOV 18 2009

.DISCUSSION...
MODIFYING TREND BEGINS TONIGHT AS ONSHORE WINDS RESUME ACROSS THE
AREA. CLEAR SKIES WILL BE REPLACED WITH CLOUDINESS FROM SW TO NE
DURING THE DAY THURS. THE NEXT STORM SYSTEM APPROACHES THE AREA ON
FRI. INCREASING MOISTURE AND LARGE SCALE LIFT WILL BE IN PLACE AS
UPPER TROF APPROACHES FROM THE WEST WHICH SHOULD RESULT IN EVENTUAL
WIDESPREAD PRECIP COVERAGE. MORE SIGNIFICANTLY THOUGH...MODELS
STILL POINTING AT A COASTAL LOW DEVELOPING SOMEWHERE IN THE
VICINITY OF MATAGORDA BAY THEN MOVES IT EWD THRU THE DAY ON FRI &
FRI NIGHT. ACTUAL POSITION OF THIS FEATURE IS CRITICAL IN REGARDS
TO RAINFALL POTENTIAL...SEVERE WX AND TIDAL ISSUES (SEE MARINE SECTION).
AS IT STANDS RIGHT NOW...IT APPEARS LOCATIONS ALONG/SOUTH OF INTERSTATE
10 (CLOSEST TO THE LOW) WILL SEE THE MOST PRECIPITATION. QPF BULLEYE`S
IN THE 5-7" RANGE HAVE BEEN COMMON AMONGST MODELS NEAR THE
COAST...WITH VALUES TAPERING OFF FURTHER INLAND. SHOULD THE LOW
HUG THE COAST AS CURRENTLY FCST THE WARM SECTOR SHOULD ALSO DO SO
OR REMAIN OFFSHORE SO SEVERE POTENTIAL SHOULD BE FAIRLY LOW
INLAND. AGAIN IT ALL HINGES ON THE SFC/LLVL LOW POSITION & TRACK.
A POSITION FURTHER NORTH WOULD SHIFT THE PROBLEMS INLAND...AND A
TRACK FURTHER SOUTH WOULD JUST FLOOD THE FISH.

WILL PROBABLY SEE SOME WRAP AROUND CLOUDS/SHRA SAT MORNING BEFORE
CLEARING ENSUES. REST OF THE WEEKEND LOOKS NICE. MEDIUM RANGE
MODELS NOT IN GOOD AGREEMENT AS TO IF AND WHEN THE NEXT FRONT
ARRIVES. DIDN`T CHANGE THE GRIDS MUCH BEYOND MON DUE TO LOW FCST
CONFIDENCE. ONGOING PACKAGE GENERALLY FOLLOWED THE GFS ADVERTISING
THE NEXT FRONT MON NIGHT OR TUE. 47

[srainhoutx]

18Z NAM Radar Sim...

http://www.nco.ncep.noaa.gov/pmb/nwprod ... loop.shtml

[wxgirl69]

How much rain are we looking at for Deer Park area? Any thoughts for the Thanksgiving weather?

[srainhoutx]

Welcome to S2k wxgirl69. Just too soon to say with any real certainty who will get the heaviest rainfall at this time. Everything will depend on the eventual track of the Upper Low and surface coastal low that is forecast to develop. Stay tuned.

[Ptarmigan]

Looks to be rainy tomorrow. I have heard Corpus Christi could get most of the rain, a good thing for them.

[srainhoutx]

Some folks between Corpus Christi and Galveston may see some very heavy rainfall...

[JenBayles]

That red bullseye is a bit too close to me for comfort. Why do these things always have to happen at night?!

[srainhoutx]

HPC Updated QPF Discussion is rather interesting concerning TX. Looks to me that there is still a lot of uncertainty concerning where the heaviest rainfall will be...

...TX...
PTNL FOR BIG RNFL IS INCRSG ACRS TX. SHRTWV TROF PUSHG THRU THE
ROCKIES IS FCST TO SPLIT WITH THE SRN PORTION DIGG INTO THE RIO
GRANDE VLY AND THE NRN PORTION CONTG TO MOV ACRS THE CNTRL U.S..
ALTHOU THE TROF SEPARATES...THIS RESULTS IN THE DVLPMENT OF A VRY
IMPRESSIVE UPR JET COUPLET/DIFL BETWEEN THE POLAR AND SBTRPCL
JETS...WITH VRY STG UPR DVRG FCST BY ALL THE GUID OVR TX LATE TNGT
INTO FRI. SVRL MDLS...GFS/ECWMF ARE SHOWG CLASSIC FEEDBACK SIGNALS
OVR THE CSTL AREAS OF TX WITH RNFL MAX IN EXCESS OF A FOOT. VRY
IMPRESSIVE AND CONCERNING SINCE THE GUID CONTS TO SHOW THIS IN STG
RUN-TO-RUN CONSISTENCY. NEG TWD THIS IS THE SREF/GEFS ENSEMBLE
SOLUS ARE SHOWG MUCH LESS PCPN AND FEWER MEMBERS WITH HVY RNFL.
THIS COULD BE A DIRECT RESULT OF THE DIFF IN GRID SPACING IN THE
OPERATIONAL MDLS VS ENSEMBLES. THE REST OF THE GUID IS SHOWG MUCH
LWR AMTS...BUT STILL QUITE HVY. PCPN IS VRY BULLS EYE
LOOKG...WHICH ALSO IS A TRADEMARK FEEDBACK SIGN. MSTR FEEDG OFF
THE GULF OF MEX SEEMS TO BE HANDLED WELL BY THE GUID SINCE THERE
IS ALRDY A LRG REGION OF PWS AOA 1.50 INCHES OVR THE WRN GULF WITH
A LINK TO THE EPAC. THIS MSTR WL CONT TO GET DRAWN NWD AS SRLY
FLOW INCRS WITH MDLS SHOWG 8H SRLY FLOW OF 30-40 KTS. THIS COULD
BE A DIRECT RESULT OF THE FEEDBACK. ALSO...THE STG SRLY 8H FLOW
RESULTS IN VRY IMPRESSIVE 8H CVRG/THERMAL FORCG ALNG THE TX CST.
MANUAL QPF SHOWS A LRG REGION OF MOD/HVY RNFL WITH SOME GRTR THAN
FIVE INCH AMTS ALNG THE IMMEDIATE TX CST. CLIMATOLOGICALLY FAVORED
1000-500 THICKNESS FOR HVY RNFL IN THIS AREA FOR NOV IS ARND 564
DM...WHICH IS LYING ACRS THE CST. THE CVNCTN COULD EASILY DVLP
FARTHER INLAND...OR EVEN PUSH QUICKLY OFFSHORE...SO AT THIS
POINT...KEPT THE HVIER RNFL RGT ALNG THE CST.

SCND AREA OF PCPN SHLD BE FOCUSED ALNG THE FNTL BNDRY THAT DVLPS
AND BEGINS TO DROP SEWD THRU TX. DEPENDING ON THE EXTENT/LAT OF
CSTL TX CNVCTN...THE MORE NRN PCPN AREA COULD BE EITHER REDUCED OR
INCRSD FM WHAT IS FCST AT THIS PT. XPCT MOD/HVY AMTS TO BE ASSOCD
WITH THE FNTL BNDRY AS IT SLOLY DROPS SEWD.

[srainhoutx]

Afternoon E-mail from Jeff...

Strong extra-tropical storm will affect the area tonight -early Saturday.

Concerns include: heavy rains, winds, storm surge/wave action

Discussion:

Strong upper level trough moving through N Mexico will move into W TX later tonight while strong upper forcing produces rapid pressure falls and surface low pressure development over the middle TX coast. Surface low pressure should develop between Rockport and Port O Connor and then move NE up the TX coast and deepen bringing adverse weather conditions and impressive winds to the coastal waters.

Rainfall:

Models are in fair agreement on the placement and track of the upper level and surface features and the resultant weather. Expect numerous thunderstorms to develop from SW to NE this evening as strong WAA above the retreating cool dome at the surface continues. Lift will also be present from the approaching upper level trough and developing surface low. A few of these storm clusters may approach severe limits especially around Matagorda Bay where the coastal warm front may move slightly inland. Widespread rains will develop by Friday morning with the heaviest rains focused along the coast and just offshore. Widespread rainfall of 1-3" with isolated amounts of 5" inches will be possible especially S of I-10. A few locations along the coast and offshore may see 6-8" of rainfall. Will need to watch for any indications of this heavy rainfall shifting inland, as amounts of this magnitude would exceed flash flood guidance and result in significant run-off issues.

Winds:

Winds are already increasing as the pressure gradient tightens between the developing low along the middle TX coast and the strong high over the SE US. Surface winds will increase and back to the E to ENE this evening. Sustained winds of 20-25mph will be likely along the coast with 15-25mph inland. As the surface low moves up the coast Friday winds will increase into the 20-35mph range with gust to 40mph or greater along the coast. Offshore waters may experience full blown gale conditions by Friday afternoon. Gale warning has been issued for the water off of Jefferson County on into LA and may be needed for our coastal waters. As the surface low passes the winds will rapidly shift N and begin to decrease into Saturday morning.

Storm Surge/Waves:

Very strong near shore winds of 30-40mph for a 12-24 hour period will produce a coastal storm surge event. Non-tropical storm surge model loaded with the GFS shows a water level rise of 1-2 feet along the coast tonight into Friday. Wave Watch III guidance shows near coastal swells building into the 8-12 foot range by Friday afternoon. The fetch is shorter than the last event, but surface winds stronger. May see total tides reach 2.5-3.5 feet above normal and this could cause issues on the W end of Galveston and Bolivar. Even higher tides and more significant flooding is possible into SW Louisiana.

Highly adverse marine conditions are expected and small craft/vessels should remain in protected bays or port on Friday.

Track of the surface system and its effects will continue to be refined this afternoon/evening and an upgraded to a coastal flood watch/warning may be required. Current thinking is that a Flash Flood Watch will not be needed, but any northward shift in the heavy rains would likely require a watch for at least a part of the forecast area.

[srainhoutx]

And HGX update "hints" at more questions than answers right now concerning where the low/trough will track...

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
248 PM CST THU NOV 19 2009

.DISCUSSION...
BASE OF TROF APPROACHING EL PASO SHOULD CONTINUE TO DEEPEN/DIG SWD
INTO CNTL & SRN TX FOR THE NEXT 24 HOURS AND EVENTUALLY KICK OUT OF SE TX
WITH A POSITIVE TILT SAT MORNING. INCREASING GULF MOISTURE AND LARGE
SCALE LIFT WILL INITIATE PRECIP OVERNIGHT WEST OF THE REGION LATER THIS
EVENING...THEN SPREADING INTO SE TX AFTER MIDNIGHT AND ON FRI. COASTAL
LOW EXPECTED TO DEVELOP SOMEWHERE BETWEEN MATAGORDA BAY AND CRP
(DEPENDING ON MODEL OF CHOICE) AND TREK EWD. WAS HOPING THE MODELS
WOULD COME INTO BETTER AGREEMENT REGARDING POSITION AND TIMING/MOVEMENT
WITH THE LOW AS IT`LL MAKE A SIGNIFICANT DIFFERENCE ON HOW INTENSE
WX WILL BECOME. INSTEAD...THERE ARE MORE QUESTIONS TODAY THAN THIS
TIME YDAY. ECMWF FURTHER S WITH THE LOW AND A BIT SLOWER...ETC
ETC ETC. FACT OF THE MATTER IS IT IS GOING TO BE WET...WITH LOCATIONS
CLOSER TO THE COAST LIKELY SEEING SOME IMPRESSIVE ACCUMULATIONS.
HAVE DECIDED TO ISSUE A FLASH FLOOD WATCH FOR AREAS SOUTH OF I-10
FOR WIDESPREAD 2-4" TOTALS WITH LOCALIZED 5-7" POSSIBLE. (MODELS
HAVE ACTUALLY BEEN SHOWING QUITE A BIT MORE ACCUMULATIONS THAN
THAT - UP TO A FOOT - BUT WITH THE MOSTLY PROGRESSIVE MOVEMENT
SUSPECT THERE MIGHT BE SOME FEEDBACK ISSUES INVOLVED.) ALSO
DECIDED TO THROW IN THE MENTION OF SEVERE RIGHT AT THE COAST BUT
THREAT WILL HINGE ON WHERE THE WARM FRONT ENDS UP. GFS AND NAM
BRING IT CLOSE ENOUGH TO THE COAST WHERE I`D BE UNCOMFORTABLE NOT
MENTIONING SOMETHING WITH FCST SOUNDINGS SHOWING IMPRESSIVE
HELICITIES.

WRAP-AROUND CLOUDS/RAIN WILL CONTINUE INTO SAT MORNING BEFORE A
GRADUAL CLEARING TREND BEGINS AND HIGH PRES BUILDS IN. REST OF THE
WEEKEND INTO THE FIRST PART OF THE WEEK LOOKS DRY/NICE AS UPPER
FLOW TRANSITIONS INTO A MOSTLY ZONAL PATTERN. ANTICIPATE THE NEXT
FRONT TUE OR WED AS TROF MOVES DOWN THE MIDWEST TOWARD THE EAST
COAST WITH RIDGING FURTHER WEST. 47

[srainhoutx]

Another e-mail from Jeff just arrived...

NWS has issued a Flash Flood Watch for areas along and S of I-10 for Friday.

Latest guidance has trended slower and wetter with this upcoming weather event while at the same time diverging on the exact track of the surface low. Regardless, QPF generated by the various guidance and the fact that KCRP is already showing numerous showers on their scope suggest that the higher amounts are more likely, but not as high as the GFS is suggesting.

Widespread rainfall of 2-4" with isolated amounts of 5-7" will be possible along and S of I-10 with amounts of 1-3" common N of I-10. Guidance has been pegging the coastal waters with 8-12" and this seems fairly aggressive given the fast nature of the event and about 18-28 hours of rainfall...not saying it won't happen. Rainfall predicted will likely exceed flash flood guidance and result in significant run-off especially in the coastal counties. The exact track of the surface low will determine where the axis of heaviest rains fall and it could be as far N as I-10 or 100 miles offshore.

Will also lean toward a slightly higher severe threat as a track of the surface low close enough to the coast could swing the warm front inland resulting in surface based rotating supercells. SPC has highlighted this in their outlook but currently is downplaying the threat to off the coast. It is a little too close of a call to not mention and any northward advance of the warm front inland would bring the threat of hail, wind, and tornadoes to that area south of the boundary.

No changes required on the marine side or with tides, but winds are already coming up and frequent gust at or over 40mph appear likely on Friday along the coast and offshore.

[JenBayles]

Drat. Looks like a long night or an early morning for everyone in Bear Creek again. ACK!

[TexasSam]

I'm a bit confused...
I know what a Tropical storm is, and a Sub-Tropical storm, but what the heck is a

Strong extra-tropical storm will affect the area tonight -early Saturday.

[srainhoutx]

I'm a bit confused...
I know what a Tropical storm is, and a Sub-Tropical storm, but what the heck is a

Strong extra-tropical storm will affect the area tonight -early Saturday.

Remember last week when Ida transitioned to ET off the East Coast and became a Noreaster? Kind of what happens in the Western Gulf as we approach the winter season. wxman57 had some comments this afternoon in Talking Tropics.

viewtopic.php?f=31&t=107076

[Flyinman]

I am very confused..Everything I read shows most heavy rain south of I-10, however a local met showed our area getting upwards of 8" by tomorrow afternoon and Brenham close to 6". I never like when there are so many different scenarios.

[JenBayles]

I'm not liking what I'm seeing on radar either. Already it seems storms to our SW are going to infiltrate well north of I-10 overnight. I'd been hoping it would be relatively quiet tonight with the big fireworks during the daylight hours. Here's hoping it moves through FAST.

[srainhoutx]

From Nesdis...

SATELLITE PRECIPITATION ESTIMATES..DATE/TIME 11/20/09 0347Z
SATELLITE ANALYSIS BRANCH/NESDIS---NPPU---TEL.301-763-8678
LATEST DATA USED: GOES-12 0315Z JN
.
LOCATION...SE TEXAS...
.
ATTN WFOS...HGX...CRP...EWX...
ATTN RFCS...WGRFC...
.
EVENT...DEVELOPING CONVECTIVE RAIN AREA
.
SATELLITE ANALYSIS AND TRENDS...LATEST GOES INFRARED IMAGERY SHOWS
RAPIDLY EXPANDING CLUSTER OF THUNDERSTORMS ALONG TX COASTLINE JUST NE
OF CRP. BLENDED TPW IMAGERY SHOWS MOISTURE PLUME EXTENDING INTO S AND
SE TX FROM WESTERN GULF OF MEXICO WITH VALUES AVERAGING 1.25-1.75". WV
IMAGERY SHOWS THAT THE THUNDERSTORMS ARE DEVELOPING IN AN AREA OF UPPER
LEVEL DIFFLUENCE BETWEEN SUBTROPICAL JET TO THE SOUTHEAST AND APPROACHING
WEAK UPPER DISTURBANCE MOVING EAST INTO TX FROM NM. THE CLUSTER APPEARS
TO BE BUILDING SOUTHWEST ALONG THE COAST AND APPEAR TO BE TRAINING OVER
THE SAME RARES. RAIN RATES OF 2.0-2.5" PER HOUR HAVE BEEN OBSERVED WITH
THE STORMS OVER COASTAL TX NEAR RKP WITH THE DEVELOPING CLUSTER. MANUALLY
DERIVED SATELLITE ESTIMATES CONFIRM THESE OBSERVED AMOUNTS THE PAST FEW
HOURS. THUNDERSTORMS WILL CONTINUE TO DEVELOP AND EXPAND IN COVERAGE
ACROSS THIS AREA THE NEXT 3-6 HOURS WITH RAIN RATES OF 2.0-2.5" POSSIBLE
DEEP MOISTURE CONTINUES TO FEED INTO THE DEVELOPING CLUSTER.

[srainhoutx]

And also Jeff just sent out another e-mail...

Weather going downhill quickly this evening.

Numerous strong to severe thunderstorms have develop from Rockport to Wharton this evening. KCRP radar already shows 6" has fallen SW of Seadrift, TX and large swath of excessive rainfall is developing NE into Matagorda Bay. Given the intense rainfall rates and PM soundings showing moisture increase to over 150% above normal...flash flood watch is warranted for sure and model QPF bombs of 8-12" may not have been feedback issues. Will hold onto the afternoon QPF numbers...but excessive rainfall and flooding is becoming increasingly likely especially along the coast.

Other big concern is tides...already 3.37ft at Galveston and rising. Long ebb tide is in progress and offshore rigs/platforms are gusting up to and over 35/40mph so water levels will continue to rise tonight into Friday. With levels already approaching 3.5 ft, feel coastal locations will have issues by Friday morning especially at Rollover and Jamaica Beach. Of note has been the constant E wind at Rockport gusting to near 40mph this evening on the north side of the surface low forming. May need to push tide forecast into the 4-5 feet above normal range Friday which is going to cause some issues on the island and in both of Galveston and Matagorda complexes.

[srainhoutx]

URGENT - IMMEDIATE BROADCAST REQUESTED
COASTAL HAZARD MESSAGE
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1008 PM CST THU NOV 19 2009

...COASTAL FLOOD WARNING IN EFFECT...

.STRONG LOW PRESSURE DEVELOPING SOUTH OF MATAGORDA BAY AREA OVERNIGHT AND
FRIDAY MORNING WILL MOVE TO THE NORTHEAST THROUGH THE UPPER TEXAS COASTAL WATERS. A TIGHTENING PRESSURE GRADIENT WILL BRING STRONG EAST TO NORTHEAST
WINDS TO THE AREA TONIGHT THROUGH FRIDAY EVENING. THE DURATION OF EAST
WINDS WILL BE ENOUGH TO DRIVE TIDES UP LEADING TO COASTAL FLOODING.
STRONG NORTHEAST TO NORTH WINDS IN THE WAKE OF THE LOW PRESSURE SYSTEM OVER THE GALVESTON BAY REGION WILL AGGRAVATE FLOODING ON THE NORTH SIDE OF GALVESTON ISLAND AND BOLIVAR PENINSULA INTO FRIDAY NIGHT.

[Ptarmigan]

Looks to be a heavy rain event tonight to Saturday. Some areas already have 7 inches of rain.