August 2016: Rain Chances Continue.

[Skyguy]

I just noticed the graphic regarding this weekend on the Houston-Galveston NWS website which I did not see earlier.

Er, how stout is that TUTT low in the graphic?

[Katdaddy]

Heavy rain across the Upper TX Coast will become a concern this weekend with a Flash Flood Watch possible. The NHC has the NW GOM flagged as a low chance of tropical development. Invest 99L looking more likely to enter the GOM but has a moderate risk of tropical development during the next 5 days. Stay weather aware through the weekend.

[cperk]

I am a bit concerned about that weak system in the north central GOM not that it could get stronger but that it could dump a lot of rain on an already soaked area.

[srainhoutx]

Friday morning briefing from Jeff:

Increasing heavy rainfall threat this weekend generally along and SE of US 59.

An upper level low over the NW Gulf will move inland over S TX today and will gradually result in the formation of a mid level and possibly surface low pressure system over the NW Gulf of Mexico this weekend. Forecast models are in some agreement on a surface low forming roughly 150 miles SE of Galveston starting late tonight and into Saturday and drifting toward the WNW this weekend and inland over the upper TX coast. Upper level winds out of the SSW and S on the eastern flank of the upper level low are currently unfavorable for development, but there could be a window on Saturday for some modest organization of this feature and NHC currently gives the system a 10% chance of formation over the next 48 hours.

Main impact of this system will be heavy to excessive rainfall as the envelop of tropical moisture associated the feature across the northern Gulf moves ashore over TX. A low level trough axis of actual surface low formation will only help to organize and concentrate excessive rainfall around a central core which would increase the flooding threat especially across the coastal counties Saturday night into Sunday. Overall system and individual storm motions will be very slow and this combined with the very moist air mass points to the potential for several inches of rainfall along and SE of the US 59 corridor over the weekend.

Grounds across the region are wet to saturated from all the recent rainfall and additional heavy rainfall over the weekend is expected to generate run-off.

99L:

Much talked about tropical wave has become extremely disorganized overnight due to strong upper level winds shear of 20-30kts over the system and dry mid level air (RH around 45%). The result of these two negative factors along with the disruption of southerly moist inflow by the higher terrain of the mountainous Caribbean Islands has resulted in an overall degradation of the feature. In fact the USAF mission for today has been cancelled and the NHC currently only gives the system a 20% chance of development over the next 48 hours as it moves generally W to WNW toward Cuba and the Florida Straits.

Development chances increase to 60% after 48 hours as the feature moves into the SE Gulf of Mexico, but is very possible that there will not be enough organization of the wave by that time for anything to develop. Interestingly, global and hurricane forecast models continue to have varying degrees of development over the eastern Gulf of Mexico along with continued various tracks. Given the overall disorganization of the feature this morning and lack of any defined low level center or “vortex” support of any of the model guidance is of very low confidence. There is some consensus that if anything does form over the SE Gulf of Mexico that it would tend to track toward the central or eastern Gulf coast.

[Rip76]

http://www.ssd.noaa.gov/goes/east/gmex/h5-loop-vis.html

Am I seeing something beginning at approx. 26N & 87W?

[Ounce]

http://www.ssd.noaa.gov/goes/east/gmex/h5-loop-vis.html

Am I seeing something beginning at approx. 26N & 87W?

I dunno. Looks like convection to me, but I know even less than enough to be dangerous.

I was curious as to why the cells west of a line from Huntsville to Freeport were moving WSW or SW, please, when there is NNW flow off the Gulf around Port Arthur.

[Ounce]

I'd guess the ULL is on land around Rosenberg because some of the cells around Sweeny are traveling SE, while the cells around Tomball are going SW. Something like that.

[srainhoutx]

UPPER TX COAST, SOUTHERN LA, & SOUTHERNMOST MS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
AN AXIS OF ABOVE NORMAL MOISTURE EXTENDS INTO THE NORTHWEST GULF
COAST ALONG THE SOUTHERN PERIPHERY OF SUBTROPICAL RIDGE, IN THE
VICINITY OF A NEARBY DISTURBANCE. WHILE THERE ARE DETAIL
DIFFERENCES IN BOTH QPF AMOUNTS AND PLACEMENT, THE GUIDANCE SHOWS
GENERAL AGREEMENT IN KEEPING HEAVIER RAIN AXIS NEAR THE IMMEDIATE
LA/UPPER TX COAST GIVEN WEDGE OF MID/UPR LEVEL DRY AIR JUST TO THE
NORTH ASSOCIATED WITH THE SUBTROPICAL RIDGE AND THE DEGREE OF
ONSHORE FLOW, WHICH SHOULD ALLOW CONVECTION TO FOCUS CLOSE TO THE
COAST PRIMARILY IN THE 06Z-15Z TIME FRAME. WITH MESOSCALE
GUIDANCE SHOWING POCKETS OF 4-7" AMOUNTS POSSIBLE, A SLIGHT RISK
OF EXCESSIVE RAINFALL IS LIKELY FOR SOUTHERN LA AND THE UPPER TX
COAST, WHICH WAS COORDINATED WITH THE LAKE CHARLES LA AND
HOUSTON/GALVESTON FORECAST OFFICES.

[srainhoutx]

Morning surface and upper air analysis suggest a trough of low pressure is near the Sabine River and a weak surface low appears to be developing South of Lake Charles. At the upper levels, a small upper low is spinning just South of Brownsville pumping up deep tropical moisture into SE Texas with at least 2 disturbances rotating toward the Upper Texas Coast.

Showers and thunderstorms should increase throughout the morning hours across the Coastal tier of Counties and extend inland later in the day. Will need to monitor the development and movement of the Coastal Low as some of the shorter term meso guidance attempt to ramp it up later today into the overnight hours as the surface low meanders generally West toward the Middle Texas Coast on Sunday. Flash Flood Watches may be required later today as some of the computer guidance suggest somewhere between 3 to 7 inches of heavy tropical rainfall may be possible over areas along and South of the I-10 Corridor today, increasing further tonight if that Coastal Low organizes a bit more than forecast. Some isolated locations closer to the Coast could see rainfall totals nearing 10 inches. Tides are also running about a foot higher than normal and tide levels could increase a bit more if the Coastal Low strengthens later today.

Not seeing much in the way of a real drying trend until possibly next Tuesday, and that will depend upon the eventual outcome of the Tropical Disturbance in the Bahamas that looks to be entering the SE Gulf of Mexico somewhere near Key West on Monday.

[unome]

https://twitter.com/iembot_hgx

Area Forecast Discussion
National Weather Service Houston/Galveston TX
633 AM CDT Sat Aug 27 2016

.AVIATION...
Storms were mainly off the coast at 1130Z. Expect these to affect the coastal sites. A more difficult forecast for terminals further inland. High resolution models differed slightly on how quickly chances for thunderstorms will increase throughout the day. Tweaked the previous forecast to delay better thunderstorm chances about an hour later due to latest model trends. The models also showed a trend toward less coverage late this evening through the overnight period. Even so, there are also indications that the sites from KHOU to the coast may experience good chances for showers and thunderstorms throughout the night.

40

&&

.PREV DISCUSSION... /ISSUED 414 AM CDT Sat Aug 27 2016/

DISCUSSION...
At 3 AM, a weak trough of low pressure was just south of the Sabine River delta. Patchy light rain continues over the northern zones with slightly stronger convection over the NW Gulf of Mexico. No discernible features at 850 MB but moisture was plentiful with 850 MB dew points between 15-17 C. A weak upper level low was noted just east of Brownsville at 300 MB. This feature shows up well on water vapor. There appears to be a plume of moisture on the east and north side of the upper low taking aim directly at SE TX. Two disturbances noted in the flow. The first disturbance should bring a round of shra/tsra to the extreme upper coast this morning, with a break this afternoon. The second disturbance will approach this evening and linger overnight. The second disturbance coupled with a developing but weak surface low over the western Gulf will accompany PW values between 2.20 and 2.35 inches and provide the area with periods of showers and thunderstorms. Areas along the coast will likely see some heavy rain tonight into Sunday. A Flash Flood Watch may be required tonight for areas near the coast. The Texas Tech WRF is particularly worrisome (it verified well yesterday) as it is stronger with the surface low and maintains a low level convergence zone over the coastal counties for a solid 24 hours. The surface feature eventually drifts southwest and away from the from the region early Monday. SW zones will likely still be affected by the slow moving surface low on Monday. Again the TT WRF is the most aggressive and continues to slowly strengthen the surface low as it moves SW along the coast. Deep moisture will continue to be pulled into the MAtagorda Bay region through Monday morning.

Even though the surface low drifts southwest, SE TX will still be influenced by a weakness aloft. PW values remain near or above 2.00 inches so scattered showers and storms expected to continue Tues-Thurs with daytime heating as the primary catalyst.

An expanding ridge over the central plains will begin to influence the region late Thursday into the weekend. Heights only build to 591-592 DM so still expect isolated showers but coverage will be considerably less. Another inverted upper trough will approach from the east next Sunday and will bring rain chances back to SE TX. 43

MARINE...
Bit of a tricky forecast. A lot will be determined on if a surface low will form during today or tomorrow. For now, a broad upper level low off the lower and mid Texas coast was helping to funnel moisture across the upper coast. A model consensus keeps easterly to east-northeasterly winds in place through Tuesday morning.

The impacts should mainly be seen in the tide levels along the coast. Current tide levels ranged from one-half to one foot above the astronomically predicted normal levels. These may rise another half a foot. Again, a lot will be determined by any surface low formation and its location and upon the strength of the surface winds. The models have been fairly consistent in developing near caution conditions today, diminishing the winds tonight through early Monday, and then redeveloping near caution conditions late Monday into early Tuesday. The seas do not look to get above 2 to 3 feet.

Mariners should continue to monitor the latest tropical weather updates from the National Hurricane Center.

40

CLIMATE...
Hobby Airport received 0.07 inches of rain yesterday and that makes 14 consecutive days with measurable rain. City of Houston Aug rainfall is up to 10.30 inches, still 6th place but only 0.44 inches shy of reaching the 4th wettest August on record.

Tropical...
A trough of low pressure over the northern Gulf is currently expected to be extratropical in nature, and the main focus should be on the rainfall potential near the coast. Still, NHC has given this area a 10 percent chance of becoming a tropical cyclone, as the upper trough could generate surface low pressure.

Farther east, Invest 99L continues to look ragged and disorganized. However, this invest should continue to be monitored. No direct impacts are forecast for SE Texas at this time. As a reminder, late August through mid September is the climatological peak of the hurricane season. Southeast Texans should make sure they keep up with the forecast and hurricane preparedness regardless of whether or not a system is in or approaching the Gulf of Mexico. 43

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 89 74 87 74 89 / 40 20 50 30 50
Houston (IAH) 88 74 87 74 88 / 40 40 60 40 50
Galveston (GLS) 86 78 86 79 86 / 70 70 70 70 60

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

$$

Discussion...43
Aviation/Marine...40

[Katdaddy]

The potential remains for very heavy rains along the coast through Sunday evening and Flash Flood Watches are likely later today. Current VIS time lapse shows a circulation S of Marsh Island, LA. Invest 99L has increasing convection just SE of the Bahamas. The tropic watch continues.

[Rip76]

The last couple of frames in this loop looks like it wants to spin up south of Galveston.

http://www.ssd.noaa.gov/goes/east/gmex/h5-loop-vis.html

[srainhoutx]

The last couple of frames in this loop looks like it wants to spin up south of Galveston.

http://www.ssd.noaa.gov/goes/east/gmex/h5-loop-vis.html

If you were to click on "Fronts" on the link you posted, you can see the trough axis sort of snakes S of Vermillion Bay. IF a surface low is developing, I would watch right at the top of that trough axis for any potential surface low to actually organize, if it does.

[Rip76]

Funny
I didn't really pay attention to that legend up top.

We must have some dry air north of us, because I would figure this feature would be firing off a few storms.

[srainhoutx]

Yes sir. There is some drier air to the North. We can thank the stout Upper Ridge for that.

[cperk]

Yes sir. There is some drier air to the North. We can thank the stout Upper Ridge for that.

srainhoutx that ridge is obvious my question is what is suppose to break that ridge down to turn 99L due north in the south east GOM.

[srainhoutx]

srainhoutx that ridge is obvious my question is what is suppose to break that ridge down to turn 99L due north in the south east GOM.

It's probably too soon to speculate on the eventual track of 99L since it has not organized and the problem I see is that the models that do develop it, send it pole ward as it deepens. So far the models have been in too much of a hurry to develop this disturbance and until there is actually a Tropical Cyclone to track, it's probably best to take the models with a grain of salt. But that's just me.

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1218 PM EDT SAT AUG 27 2016

VALID 12Z TUE AUG 30 2016 - 12Z SAT SEP 03 2016

...OVERVIEW/UNCERTAINTY ASSESSMENT...

MODELS ARE IN VERY GOOD AGREEMENT WITH THE LARGE SCALE EVOLUTION
OF FLOW OVER THE LOWER 48 NEXT WEEK...WHICH SHOULD FEATURE A
CENTRAL U.S. RIDGE SURROUNDED BY A BROAD UPPER TROUGH CARVING OUT
OVER THE GREAT LAKES/NORTHEAST AND A RELATIVELY SHARPER TROUGH
AMPLIFYING OVER THE WESTERN U.S. THE WPC DAY 3-7 FORECAST
STARTED WITH A GENERAL CONSENSUS BLEND TO BEST SMOOTH OUT SOME OF
THE DETAIL DIFFERENCES WITH EMBEDDED SHORTWAVE ENERGY IN THE
EASTERN U.S. TROUGH AND SOME TIMING DIFFERENCES WITH THE INLAND
PROGRESSION OF THE WESTERN U.S. TROUGH LATE NEXT WEEK.

ON THE FLIP SIDE...THE UNUSUALLY LARGE AMOUNT OF MODEL SPREAD AND
UNCERTAINTY CONTINUES WITH THE FORECAST OVER THE SOUTHEAST AND
GULF COAST STATES. THE RANGE OF SOLUTIONS BETWEEN DETERMINISTIC
GUIDANCE AND INDIVIDUAL ENSEMBLE MEMBERS SUGGESTS CONFIDENCE IN
ANY SCENARIO IS QUITE LOW. THE NATIONAL HURRICANE CENTER IS
CURRENTLY MONITORING THREE AREAS FOR POSSIBLE DEVELOPMENT THAT
COULD IMPACT THE U.S....ONE JUST SOUTH OF THE BAHAMAS...A SECOND
IN THE WESTERN GULF OF MEXICO...AND A THIRD SOUTHWEST OF BERMUDA
(FOR THE LATEST INFORMATION PLEASE REFER TO http://WWW.NHC.NOAA.GOV).


...WEATHER HIGHLIGHTS/THREATS...

LOCATIONS FROM THE GULF COAST THROUGH FLORIDA AND THE SOUTHEAST
COAST SHOULD CONTINUE TO MONITOR THE POTENTIAL FOR HEAVY RAINFALL
DEPENDING ON HOW INDIVIDUAL FEATURES EVOLVE OVER THE GULF OF
MEXICO AND OFF THE SOUTHEAST COAST. ELSEWHERE...SHOWERS AND
THUNDERSTORMS WILL BE POSSIBLE WITH A COLD FRONT PRESSING FROM THE
GREAT LAKES TO THE NORTHEAST TUESDAY-THURSDAY...AND ABOVE NORMAL
TEMPERATURES AHEAD OF THE BOUNDARY SHOULD RETURN TO NORMAL OR
BELOW NORMAL AS SURFACE HIGH PRESSURE BUILDS IN BEHIND THE FRONT.
THE AMPLIFYING WESTERN U.S. TROUGH SHOULD KEEP DAY TIME
TEMPERATURES BELOW NORMAL ALONG THE WEST COAST...WHILE THE
DOWNSTREAM RIDGING SHOULD BRING ABOVE NORMAL TEMPERATURES TO THE
NORTH CENTRAL U.S..


GERHARDT

[DoctorMu]

Uncertainty yields a EuroBomb over Mobile in the 12Z @ hr 168.




A wary eye out for anyone on the Gulf coast...

GFS still skeptical of any significant development.

[DoctorMu]

Muchos uncertainty remains.







The consensus appears to be tropical storm, somewhere along the Gulf Coast

[DoctorMu]

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT SAT AUG 27 2016

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Tropical
Storm Gaston, located more than 700 miles east-southeast of Bermuda.

1. A weak area of low pressure located between the northern coast of
Cuba and Andros Island in the Bahamas continues to produce a large
area of disorganized showers and thunderstorms, mainly to the south
and east of its center. Upper-level winds are not conducive for
significant development during the next day or so while the low
moves west-northwestward through the Straits of Florida at about 10
mph. Environmental conditions could become a little more conducive
for some development when the system moves into the eastern Gulf of
Mexico early next week. Heavy rains are likely to continue over
portions of eastern and central Cuba today. Gusty winds and locally
heavy rainfall are likely over portions of the Bahamas, and will
spread into parts of southern Florida and the Florida Keys by
Sunday. Interests elsewhere in Florida and the eastern Gulf of
Mexico should continue to monitor the progress of this disturbance.
The Hurricane Hunter aircraft mission scheduled to investigate this
system today has been canceled.
* Formation chance through 48 hours...low...30 percent
* Formation chance through 5 days...medium...40 percent

2. A broad area of low pressure located about 140 miles southwest of
Bermuda is producing winds of 30 to 35 mph. Shower and thunderstorm
activity has not become any better organized during the past few
hours, and significant development of this system is likely to be
slow to occur due the proximity of dry air during the next couple of
days while it moves westward and then west-northwestward at about
10 mph toward the coast of North Carolina. After that time,
increasing vertical wind shear is expected to make development
unlikely. For additional information on this system, see High Seas
Forecasts issued by the National Weather Service.
* Formation chance through 48 hours...low...30 percent
* Formation chance through 5 days...low...30 percent

3. A weak trough of low pressure located south of the coast of
southwestern Louisiana is producing disorganized shower and
thunderstorm activity over the north-central Gulf of Mexico.
Conditions are not expected to be conducive for development before
this system reaches the coast of Texas on Sunday. However, heavy
rainfall is possible along the Gulf Coast from Louisiana to
southeastern Texas during the next few days. For additional
information, please see products from your local National Weather
Service office.
* Formation chance through 48 hours...low...near 0 percent
* Formation chance through 5 days...low...near 0 percent