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SEPTEMBER 2018 - Very Wet Month Wrap Up

General Weather Discussions and Analysis

Re: SEPTEMBER 2018 -Wet Weekend/Tracking The Tropics

Postby srainhoutx » Sun Sep 09, 2018 8:03 am

Sunday morning briefing from Jeff:

Threat for heavy rainfall and flooding will be increasing over SE TX today through Tuesday.

Flash Flood Watches will likely be required for portions of the area…possibly as soon as today.

Several ingredients continue to come together that will likely result in periods of heavy to excessive rainfall across SE TX starting today and lasting into the early part of the week…in fact it looks wet through much of the next 5 days. A slow moving frontal boundary currently along a line from near Lufkin to Brenham to San Antonio will drift southward today and combine with deep tropical moisture in place (PW 2.1-2.3 inches). Thus far the lack of good low level inflow (flow of gulf moisture into the region) and sustained large scale lift has helped keep rainfall more scattered than widespread over SE TX. This appears to change tonight into Monday and Tuesday as an upper level trough gradually develops over the region helping to provide additional lift and the potential for the formation of convective induced areas of low pressure (MVC…meso vorticity center) to focus, train, and sustain rainfall.

Over time the frontal boundary which is already weak…will lose its definition and transition into more of a near inland coastal trough which will establish along a line roughly from Matagorda Bay to NW Galveston Bay and provide as focus for storm formation. Flash flooding has already been produced by this setup over central and north Texas both yesterday and again overnight. While there is no strong signal pointing toward a widespread flood threat over the area…several of the ingredients that have historically produced excessive rainfall and flooding over SE TX will be in place over the next few days.

Rainfall totals today-Tuesday could average 1-3 inches with isolated amounts of 4-5 inches. These totals could be on the low side especially if any areas of sustained training were to develop in such a tropical air mass that is in place. Grounds are not as dry as they were last week as the area has seen several days of scattered showers and thunderstorms so the run-off potential will be increasing.
Carla/Alicia/Jerry(In The Eye)/Michelle/Charley/Ivan/Dennis/Katrina/Rita/Wilma/Humberto/Ike/Harvey

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Re: SEPTEMBER 2018 -Wet Weekend/Tracking The Tropics

Postby Rip76 » Sun Sep 09, 2018 9:03 am

That area south of Cuba looks very interesting.
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Re: SEPTEMBER 2018 -Wet Weekend/Tracking The Tropics

Postby don » Sun Sep 09, 2018 9:11 am

Yes, several of the Euro ensembles develop it north of the Yucatan this week

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Re: SEPTEMBER 2018 -Wet Weekend/Tracking The Tropics

Postby srainhoutx » Sun Sep 09, 2018 9:53 am

GOES 16 Water Vapor imagery suggests that wind shear is an inhibiting factor for that area of disturbed weather nearing the Western Caribbean Sea. You'll notice a TUTT (Tropical Upper Tropospheric Trough) meandering generally West from the Eastern Gulf. Conditions may be come a bit more hospitable as the twave enters the Bay of Campeche next week.

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Carla/Alicia/Jerry(In The Eye)/Michelle/Charley/Ivan/Dennis/Katrina/Rita/Wilma/Humberto/Ike/Harvey

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Re: SEPTEMBER 2018 -Wet Weekend/Tracking The Tropics

Postby ticka1 » Sun Sep 09, 2018 9:59 am

Rip76 wrote:That area south of Cuba looks very interesting.



I just saw that is it a low pressure or upper level low?
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Re: SEPTEMBER 2018 -Wet Weekend/Tracking The Tropics

Postby srainhoutx » Sun Sep 09, 2018 9:59 am

Tough forecast for our Area with many of the meso models performing very poorly. HGX is sticking with the likelihood of a potential Heavy Rainfall Event over the next 36 to 48 hours. Keep weather aware and stay away from any high water!

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1053 AM CDT SUN SEP 9 2018

.UPDATE...
GEARING UP FOR WHAT WILL LIKELY BE A COUPLE OF ACTIVE DAYS AS
PERIODS HIGH RAINFALL RATES INCREASE THE TOTAL PRECIPITATION
ACCUMULATION AND ULTIMATELY THE FLASH FLOOD THREAT. DUE TO DRY
10-40CM DEPTH SOIL, MANY CAN HANDLE A QUICK 1 TO 2 INCH PER HOUR
RATES. IT IS WHEN WE BEGIN EXPERIENCING GREATER THAN PER 2 INCH
PER HOUR RATES THAT URBAN STREETS AND LOW LYING (RURAL ROADS)
AREAS WILL BEGIN TO FLOOD. THE OVERALL FORECAST IS FOR AREAWIDE
LIKELY RAIN CHANCES WITH THE MAIN NEAR AND SHORT TERM CHALLENGES
BEING ON WHERE THESE POCKETS OF GREATER THAN 2 INCH TOTALS WILL
EVOLVE TODAY/MONDAY. A COASTAL TROUGH IS ALREADY IN PLACE AND AIR
MASS MOISTURE WAS ABOVE THE 75 PERCENTILE (CLIMATOLOGICALLY) AT
2.0 TO 2.2 INCH PRECIPITABLE WATERS. THE NWP HIGHER RESOLUTION
MODELING WANTS TO FORM AN MCV-LIKE FEATURE ALONG THE COASTAL BEND
WITH MANY OF THE MEMBERS PEGGING BOTH THE COASTAL COUNTIES (COASTAL
TROUGHING/MCV?) AND THE NORTHERN TIER COUNTIES (VICINITY OF A
STATIONARY BOUNDARY) AS THE MAIN FOCUS AREA FOR CLUSTERS OF
HIGHER PRECIPITATION. THERE ARE MANY FACTORS THAT ARE KEEPING US
UNDER THE GUN FOR A POTENTIAL FLOOD EVENT IN THE NEXT 36 TO 48
HOURS...ONE BEING BETTER UPPER LEVEL FORCING. THE SLOW EASTWARD
PROGRESSION OF THE UPPER LEVEL TROUGH (AXIS OVER EASTERN OK THIS
MORNING) AND AN APPROACHING 25H SPEED MAX, ALONG WITH WEAK NE
TEXAS 25-3H DIFFULENCE, SUGGEST AN INCREASING PROBABILITY OF THE
OVERALL ENHANCEMENT OF AREAWIDE RAINFALL WITH LOCALLY HEAVY
DOWNPOURS THROUGH AT LEAST TUESDAY. OF COURSE, WHATEVER OCCURS
TODAY WILL DETERMINE WHAT OCCURS TOMORROW AND SO FORTH AND SO ON.
AS OF NOW, STICKING TO A HIGH POP/RELATIVELY HIGH QPF FORECAST THAT
WILL BE FOCUSED ACROSS THE THE COASTAL AND FAR NORTHERN COUNTIES
TODAY, THEN TRANSITION INTO THE CENTRAL CWA COUNTIES THROUGH MONDAY
AFTERNOON. WE WILL BE MONITORING THE ONGOING ACTIVITY OVER THE NEXT
6 HOURS TO DETERMINE WHETHER WE NEED TO ISSUE A FLASH FLOOD WATCH
OVER MORE AT-RISK COUNTIES. 31
Carla/Alicia/Jerry(In The Eye)/Michelle/Charley/Ivan/Dennis/Katrina/Rita/Wilma/Humberto/Ike/Harvey

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Re: SEPTEMBER 2018 -Wet Weekend/Tracking The Tropics

Postby Ptarmigan » Sun Sep 09, 2018 11:30 am

ticka1 wrote:
Rip76 wrote:That area south of Cuba looks very interesting.



I just saw that is it a low pressure or upper level low?


Atlantic Tropical Weather Discussion
https://www.nhc.noaa.gov/text/refresh/M ... WDAT.shtml?

Code: Select all
...DISCUSSION...

GULF OF MEXICO...

An upper level low is centered over the E Gulf of Mexico near
25N87W. Scattered showers are E of 87W. An upper level ridge is
over the W Gulf W of 92W with northerly upper level flow.
Scattered showers are over the NW Gulf and the Texas coast W of
94W. At the surface, 5-10 southerly flow covers the Gulf.

Weak ridging from the Carolinas to the Texas coast will shift N
over the SE United States. A trough will move west off the Yucatan
coast each evening and dissipate over the SW gulf each morning.
The trough will be accompanied by moderate to fresh winds.

CARIBBEAN SEA...

A large upper level high is centered over the central Caribbean
near 16N75W. A tropical wave is the main source of convection in
the W Caribbean. See above.

Isaac is forecast to approach the Lesser Antilles as a hurricane
Thursday, and continue into the eastern Caribbean Friday. A
relatively weak surface ridge in the western Atlantic Ocean will
maintain moderate to fresh trade winds over most of rest of the
region through Monday night. Building high pressure in the eastern
Gulf of Mexico will allow fresh to locally strong E to SE winds
and building seas in parts of the NW Caribbean Sea from Sunday
through Tuesday.

ATLANTIC OCEAN...

Please read the SPECIAL FEATURES section for details about
T.S. Florence, T.S. Isaac, and T.S. Helene.

Isolated moderate convection is over the W Atlantic from 26N-30N
between 72W-79W to include the N Bahamas. A small 1016 mb high is
over the W Atlantic near 25N68W. A small upper level low is near
30N70W. A 1013 mb low is centered near 30N70W. A 1025 mb high is
over the E Atlantic near 34N27W.

For additional information please visit
http://www.hurricanes.gov/marine

$$
Formosa


Looks like a tropical wave.
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Re: SEPTEMBER 2018 -Wet Weekend/Tracking The Tropics

Postby unome » Sun Sep 09, 2018 11:44 am

Ptarmigan wrote:Looks like a tropical wave.


si
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Re: SEPTEMBER 2018 -Wet Weekend/Tracking The Tropics

Postby srainhoutx » Sun Sep 09, 2018 12:01 pm

Sunday afternoon briefing from Jeff regarding Disturbed Weather in the NW Caribbean Sea:

Tropical wave over the NW Caribbean Sea is showing signs of better organization today.

NHC 200pm Tropical Weather Outlook now places a 20% chance of tropical cyclone formation from this wave across the central and western Gulf of Mexico this week. While deep thunderstorm activity has developed with this wave axis, there are no signs of any closed low level circulation and upper level winds at least for the next 1-2 days will likely prevent any sort of sustained development. However, as this feature moves WNW/NW into the central Gulf of Mexico upper level winds are forecasted to become increasingly favorable for development.

A review of global model guidance and ensemble trends do show some modest support from both the operational and ensemble members for tropical cyclone formation over the Gulf of Mexico. The same large scale blocking high pressure system that will be forcing Florence toward the SE US will also likely force any Gulf development toward the WNW/NW or toward the western/northwestern Gulf of Mexico this week.

Residents along the TX coast should maintain a close watch on this feature over the coming days.
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Re: SEPTEMBER 2018 -Wet Weekend/Tracking The Tropics

Postby srainhoutx » Sun Sep 09, 2018 12:39 pm

The 12Z ECMWF suggests a weak surface low attempts to organize just off the Middle Texas Coast next Friday morning
Carla/Alicia/Jerry(In The Eye)/Michelle/Charley/Ivan/Dennis/Katrina/Rita/Wilma/Humberto/Ike/Harvey

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