ATL: INVEST 94L - DISCUSSION

[Ptarmigan]

Just took a look at sfc obs in the region. Winds are down and pressures are slightly up around the disturbance. Convection/convergence remain quite weak. Threat to Gulf may be increasing, though. But if the threat is mostly rain, then that won't be bad.

Longer it takes time, better for us. If it developed sooner, it would be under the influence of high pressure and push it northeastwards.

[gatorcane]

The strong mid/upper level circ is displaced at least 100 nmi east of the LLCC. That is severe decoupling. Perhaps the M/U circ can bore down to the surface, but it isn't likely. My thinking is the 400 mb flow (still nwly at 12Z at Cayman) to turn easterly for about 12 hr or so on Monday afternoon and evening, which would allow for the two circs to become aligned before the mid to upper flow turns back swly north of 20N and  shears the system apart with the remnant LLCC moving nnwd just west of FL...which will FINALLY kick in the rainy season.

Your thinking is reasonable. We do need a kick to the rainy season as dew points at the major terminals in south Florida are still below 70f. I think that this system may give it a kick and deep se flow will setup. The convection should stay well to the northeast as sw shear will impact the system as it moves north. Here in the Bahamas, things are very dry so rains from 94L will be welcome.

[SouthDadeFish]

Can anyone explain this? This is the 200mb vorticity showing an upper level low developing S of 94L:

[Nederlander]

On my phone so I can't post an image but strong convection firing up just south of western jamaica..

[gatorcane]

Indeed. Very cold cloud tops are now visible in ir. Looks like very big thunderstorms are blowing up just east of the surface low as dmax is approaching. If this keeps up, could be a large blob of convection by the morning. Plus it is getting a comma shape to it, which indicates the structure continues to gradually improve.

[PTrackerLA]

Very cold cloud tops developing south of Jamaica with the MLC, should be interesting to see what happens tomorrow. Hopefully this situation evolves to be a big rain producer for some along the gulf coast...we ALL could use it badly!

[SFLcane]

The strong mid/upper level circ is displaced at least 100 nmi east of the LLCC. That is severe decoupling. Perhaps the M/U circ can bore down to the surface, but it isn't likely. My thinking is the 400 mb flow (still nwly at 12Z at Cayman) to turn easterly for about 12 hr or so on Monday afternoon and evening, which would allow for the two circs to become aligned before the mid to upper flow turns back swly north of 20N and  shears the system apart with the remnant LLCC moving nnwd just west of FL...which will FINALLY kick in the rainy season.

Your thinking is reasonable. We do need a kick to the rainy season as dew points at the major terminals in south Florida are still below 70f. I think that this system may give it a kick and deep se flow will setup. The convection should stay well to the northeast as sw shear will impact the system as it moves north. Here in the Bahamas, things are very dry so rains from 94L will be welcome.

As far as the rainy season start, yes dewpoints have been lower than normal, which of course we don't expect to see this time of year. We have already had a few periods of higher dewpoints going back to mid-April which have lasted several days in a row, but mixed in with these late dry periods. The start of the rainy season can be modified after the fact, it's not something that is set in stone once it's "officially" declared. Some years it's easy, some it's hard (like this year). In the end, it's not really that big of a deal to try to pin down the exact date it starts, but its impacts once it does start.

BTW, the 70 degree dewpoint criteria is one that was never proven scientifically in my opinion. We have to think of these things scientifically, and it's probable that a dewpoint of 67 or 68 could be just as important as 70. That's why I don't place great emphasis on the 70 degree dewpoints. Insteadweed should start to look at other things such as precipitable water in the lower levels of the atmosphere, instability, sea surface temperatures, etc.

[JonathanBelles]

My current thoughts on the system: http://jonathanbelles.wordpress.com

94L is a fighter and it will be interesting to see what happens tomorrow.

[Rgv20]

Quite a change by the 0z CMC it takes 94L east of Florida.

http://moe.met.fsu.edu/cgi-bin/cmctc2.cgi?time=2011060600&field=Sea+Level+Pressure&hour=Animation

[Gustywind]

2 AM EDT TWO= Remains at 40%

000
ABNT20 KNHC 060541
TWOAT

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 AM EDT MON JUN 6 2011

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

A LARGE BUT DISORGANIZED AREA OF DISTURBED WEATHER ASSOCIATED WITH A
BROAD AREA OF LOW PRESSURE CONTINUES OVER A LARGE PORTION OF THE
CENTRAL AND WESTERN CARIBBEAN SEA. THE AREA OF LOWEST PRESSURE IS
LOCATED ABOUT 175 MILES SOUTH OF GRAND CAYMAN AND REMAINS SEPARATED
FROM THE STRONGEST THUNDERSTORM ACTIVITY. HOWEVER...SOME
DEVELOPMENT OF THIS SYSTEM IS POSSIBLE DURING THE NEXT DAY OR SO
BEFORE UPPER-LEVEL WINDS BECOME UNFAVORABLE. THERE IS A MEDIUM
CHANCE...40 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS. AN AIR FORCE RESERVE HURRICANE HUNTER
AIRCRAFT IS SCHEDULED TO INVESTIGATE THE SYSTEM LATER TODAY...IF
NECESSARY. REGARDLESS OF DEVELOPMENT... HEAVY RAINS COULD CAUSE
FLASH FLOODS AND MUD SLIDES OVER PORTIONS OF HAITI AND JAMAICA AS
THE SYSTEM MOVES SLOWLY TOWARD THE NORTHWEST OR NORTH OVER THE NEXT
COUPLE OF DAYS.

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

$$
FORECASTER AVILA

[KWT]

http://www.ssd.noaa.gov/goes/flt/t2/flash-avn.html


there is your refire as if it was listening to you guys......very close to the center with some cold tops....

Yeah good convective burst, its almost like you can time this systems weakening/bursting phases.

[jlauderdal]

On my phone so I can't post an image but strong convection firing up just south of western jamaica..

i always knew those texans were unable to multitask

a weak yet broad low getting into the se gulf would be a very good setup for everyone doing the rain dance


"because winds are calm and very light"-Lissette Gonzalaz, weather girl CBS 4 Miami 6/6/2011

[GCANE]

Not bad on IR and ASCAT.

Wind field looks like a TD.

[wxman57]

Definitely looks less organized since yesterday afternoon. Winds in the region are down, and LLC is less evident. Buoy west of Jamaica has a very light SW wind. NHC put the center east of the buoy, which doesn't fit with its obs. I have it just west of the buoy (if there is one). All convection is well off to the east, and there is no sign of an LLC reformation closer to the convection. Convection remains quite weak.

[Nimbus]

The ULL over the Bay of Campeche has gone stationary so until that lifts out or moves northwest the light shear may continue. Doesn't take much shear to keep the LLC naked when the surface pressure is so broad.

[NDG]

I agree with you wxman57, broad low center has to be very close or NNW of the buoy which as you say has been reporting S to W winds for the past 6 hours or so, even with pressure down 1006mb as reported by the buoy it looks very disorganized, in between two blobs of convection far away from the center.
Surface circulation has continued its track westward very slowly leaving a MLC south of Jamaica.

[GCANE]

[NDG]

Now that the broad low pressure center is approaching an area of UL divergence, convection is firing up in its NW quadrant, thanks to the ULL in the GOM. It will be interesting to see what happens during the day today if actually slightly higher shear may help the system more than anything over the next 24-48 hrs.

I put the L where I believe the surface low pressure is.

[GCANE]

Getting some overshooting tops. Rain-rate has been moderate to heavy for about 2 hrs.

[GCANE]

RUC sounding near NHC's tagged COC shows air saturated thru about 500mb.