Model Runs & Discussions of GOM-Bahamas

[jasons2k]

From Jeff Lindner:

Pieces starting to come together for potential Gulf tropical development.

A broad area of low pressure has formed over the Bahamas N along the FL E coast where surface pressures have fallen 2mb in the last 24 hours along with an increase in shower and thunderstorm activity. This system is in combination with an upper level low that has formed over C FL near Tampa as is clear on the water vapor. Since we now have a large area of lower pressures I feel more confident in the model solutions of tropical cyclone formation.

A review of the main guidance this morning does not show much change from the past few days. Only the CMC is wildly different taking the system N into the SE US which seems unreasonable given building heights…only way this could really happen is if the system were to ramp up fairly quickly and given the less than ideal upper air pattern I do not see that happening. The NOGAPS drives a surface low SW into the southern Gulf as it has stronger ridging over the southern US while the GFS, EURO, ECMWF, and UKMET all aim the system at TX and LA. Upper TX coast seems to be the most favored location today on the 00Z model runs with the UKMET aimed at Freeport, the GFS near High Island, and the EURO near Matagorda Bay. Given the upper air pattern that will be at hand this weekend a general W to WNW track with a slowing of forward speed looks good. Forecast toward the end of the period hinge on the ridge intensity over the southern US and the strong cut-off low over S CA coast. If the low shears out like the GFS then the western edge of the ridge will weaken allowing the Gulf system to turn more northward toward the upper TX or LA coast. If the low is slower to eject or even retrogrades some then the ridge will intensify over the southern plains likely forcing the Gulf system more westward toward the middle or lower TX coast or even SW toward MX.

As far as intensity goes none of the models show much intensification. Since the system will be moving within decent closeness of the upper TUTT and unfavorable 300mb shear is possible over the system preventing deepening. However, global models are not great at intensity forecasting as the GFS had Felix as an open wave when it was a cat 5 so I will only put so much faith in their ability to forecast intensification. Based on the current track being provided from the various guidance the system should interact with the warm Gulf loop current where past storms have developed at an extremely fast rate. Although SST’s are at 85 or above across the Gulf if the upper air pattern is not favorable the system will struggle. For now will go with a weak tropical storm in the central Gulf by Saturday.

Residents along the Gulf coast from the MS River westward should keep a close watch on the ongoing developments in the tropics late this week into this weekend.

Significant changes to the current forecast may be needed as surface winds of 5-10mph for Sunday and seas of less than 2ft which are currently being forecast would be way too low should something spin

[flwxwatcher]

000
ABNT20 KNHC 181523
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1130 AM EDT TUE SEP 18 2007

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

A LARGE AREA OF CLOUDINESS AND THUNDERSTORMS EXTENDS FROM THE EAST
COAST OF FLORIDA EASTWARD FOR A FEW HUNDRED MILES OVER THE WESTERN
ATLANTIC AND BAHAMAS. THIS ACTIVITY IS ASSOCIATED WITH AN
UPPER-LEVEL LOW OVER THE FLORIDA PENINSULA AND A TROPICAL WAVE OVER
THE NORTHWESTERN BAHAMAS. THIS SYSTEM HAS THE POTENTIAL FOR
SUBTROPICAL OR TROPICAL CYCLONE FORMATION OVER THE NEXT COUPLE OF
DAYS AS IT MOVES WESTWARD OVER FLORIDA AND INTO THE EASTERN GULF OF
MEXICO. LOCALLY HEAVY RAINFALL IS POSSIBLE OVER PORTIONS OF THE
FLORIDA PENINSULA AND THE BAHAMAS DURING THE NEXT DAY OR TWO.

THE REMNANTS OF TROPICAL DEPRESSION INGRID...A TROUGH OF LOW
PRESSURE...EXTEND FROM THE EASTERN CARIBBEAN SEA NORTHWARD ACROSS
THE NORTHERN LEEWARD ISLANDS INTO THE ATLANTIC. REDEVELOPMENT IS
NOT EXPECTED DURING THE NEXT COUPLE OF DAYS AS THIS SYSTEM MOVES
SLOWLY NORTHWESTWARD.

SHOWER ACTIVITY REMAINS LIMITED IN ASSOCIATION WITH A TROPICAL WAVE
LOCATED ABOUT 700 MILES EAST OF THE LESSER ANTILLES. UPPER-LEVEL
WINDS ARE BECOMING LESS FAVORABLE...AND ANY DEVELOPMENT OF THIS
SYSTEM IS EXPECTED TO BE SLOW TO OCCUR AS IT CONTINUES WESTWARD AT
10 TO 15 MPH.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$

FORECASTER BEVEN

If this system does end up getting named I wouldn't be surprised for it to be a subtropical Storm , at least in its initial stages.

[CrazyC83]

ABNT20 KNHC 181523
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1130 AM EDT TUE SEP 18 2007

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

A LARGE AREA OF CLOUDINESS AND THUNDERSTORMS EXTENDS FROM THE EAST
COAST OF FLORIDA EASTWARD FOR A FEW HUNDRED MILES OVER THE WESTERN
ATLANTIC AND BAHAMAS. THIS ACTIVITY IS ASSOCIATED WITH AN
UPPER-LEVEL LOW OVER THE FLORIDA PENINSULA AND A TROPICAL WAVE OVER
THE NORTHWESTERN BAHAMAS. THIS SYSTEM HAS THE POTENTIAL FOR
SUBTROPICAL OR TROPICAL CYCLONE FORMATION OVER THE NEXT COUPLE OF
DAYS AS IT MOVES WESTWARD OVER FLORIDA AND INTO THE EASTERN GULF OF
MEXICO. LOCALLY HEAVY RAINFALL IS POSSIBLE OVER PORTIONS OF THE
FLORIDA PENINSULA AND THE BAHAMAS DURING THE NEXT DAY OR TWO.

It's quite rare that you see that from something not an Invest...

[Portastorm]

12z GFS run at 36hrs:

http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_036l.gif

(low just off SW Florida coast)

[ronjon]

I would expect an investigation today for the Bahamas low.

[jhamps10]

ABNT20 KNHC 181523
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1130 AM EDT TUE SEP 18 2007

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

A LARGE AREA OF CLOUDINESS AND THUNDERSTORMS EXTENDS FROM THE EAST
COAST OF FLORIDA EASTWARD FOR A FEW HUNDRED MILES OVER THE WESTERN
ATLANTIC AND BAHAMAS. THIS ACTIVITY IS ASSOCIATED WITH AN
UPPER-LEVEL LOW OVER THE FLORIDA PENINSULA AND A TROPICAL WAVE OVER
THE NORTHWESTERN BAHAMAS. THIS SYSTEM HAS THE POTENTIAL FOR
SUBTROPICAL OR TROPICAL CYCLONE FORMATION OVER THE NEXT COUPLE OF
DAYS AS IT MOVES WESTWARD OVER FLORIDA AND INTO THE EASTERN GULF OF
MEXICO. LOCALLY HEAVY RAINFALL IS POSSIBLE OVER PORTIONS OF THE
FLORIDA PENINSULA AND THE BAHAMAS DURING THE NEXT DAY OR TWO.

It's quite rare that you see that from something not an Invest...

my guess is that we see invest soon, maybe early afternoon.

[Portastorm]

12z GFS at 48 hrs:

http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_048l.gif

(1010mb low off west coast of Florida)

[Portastorm]

12z GFS run at 60hrs:

http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_060l.gif

(now a 1008 mb low slowly migrating west into the eastern GOM)

[skysummit]

Whoa....check out the upper levels at 54 hours:
200mb winds

[hcane27]

For what it's worth department ..... posted with special permission from Hurricane Alley

['CaneFreak]

LOOK AT THESE UL WINDS!!!! Totally different than last night. Much less on the order of 10-15 knots.

http://www.nco.ncep.noaa.gov/pmb/nwprod ... 0_066m.gif

[Chacor]

Not sure if this was posted...

NOUS42 KNHC 181330
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
0930 AM EDT TUE 18 SEPTEMBER 2007
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 19/1100Z TO 20/1100Z SEPTEMBER 2007
TCPOD NUMBER.....07-116

I. ATLANTIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. SUCCEEDING DAY OUTLOOK: PROBABLE LOW LEVEL INVEST
NEAR 25.5N 88.0W AT 20/1800Z.

II.PACIFIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. OUTLOOK FOR SUCCEEDING DAY.....NEGATIVE.
JWP

Notice how it says "probable" and not "possible".

[Wx_Warrior]

Help a brother out....Strong ULW mean....?

[skysummit]

Upper level support is looking pretty darn good in this run.

['CaneFreak]

Help a brother out....Strong ULW mean....?

Upper level winds

[jhamps10]

12z GFS run at 60hrs:

http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_060l.gif

(now a 1008 mb low slowly migrating west into the eastern GOM)

and it looks like the upper level winds are a LOT less than in 00z run. in a word, not good for wherever it wants to take this....

[Wx_Warrior]

I know that much...What does that mean development/hinder/movement for this thing?

[skysummit]

12z GFS run at 60hrs:

http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_060l.gif

(now a 1008 mb low slowly migrating west into the eastern GOM)

and it looks like the upper level winds are a LOT less than in 00z run. in a word, not good for wherever it wants to take this....

No kidding....this run is sucking so far. If the GFS is correct on this upper level environment, it may be much stronger than what some of us are currently thinking.

['CaneFreak]

I know that much...What does that mean development/hinder/movement for this thing?

Favorable conditions for strengthening. Doesn't mean anything for movement or much else.

[jhamps10]

I know that much...What does that mean development/hinder/movement for this thing?

Favorable conditions for strengthening aloft. Doesn't mean anything for movement or much else.

WAIT a minute here canefreak, I thought high ULW meant shear, and in turn would be very unfavorable for development.... am I wrong on that.