Issac-Prep/Obs/Haiti/DR/Cuba/Bahamas/Keys/Florida Pen/PH

[GCANE]

MESOSCALE DISCUSSION 1813
NWS STORM PREDICTION CENTER NORMAN OK
0605 AM CDT SUN AUG 26 2012

AREAS AFFECTED...PORTIONS SRN FL AND KEYS.

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 261105Z - 261330Z

PROBABILITY OF WATCH ISSUANCE...95 PERCENT

SUMMARY...TORNADO POTENTIAL WITH ISAAC IS FCST TO INCREASE THROUGH
REMAINDER MORNING INTO AFTN. THREAT SHOULD START AS MRGL DURING
NEXT 1-2 HOURS...BUT INCREASE WITH TIME. AS SUCH...TORNADO WW MAY
BE REQUIRED WITHIN NEXT 1-2 HOURS AND IS QUITE LIKELY SOMETIME THIS
MORNING. ALSO...IN UPCOMING 13Z DAY-1 OUTLOOK...TORNADO
PROBABILITIES WILL BE INCREASED FOR S FL...WITHIN BROADER
CATEGORICAL SLGT RISK.

DISCUSSION...TC TORNADO THREAT IS MRGL ATTM...BUT WILL RAMP UP AND
EXPAND NWWD ACROSS AREA TODAY AS THESE PROCESSES TAKE PLACE LARGELY
IN TANDEM...

1. CENTER OF ISAAC PASSES S OF MAINLAND...ACROSS LOWER KEYS INTO
EXTREME ERN GULF...BASED ON LATEST NHC TRACK FCST. THIS WILL
TRANSLATE FAVORABLE NERN SECTOR OF CYCLONE ACROSS DISCUSSION AREA.

2. STRENGTHENING/EXPANDING LOW-LEVEL WIND FIELDS...PER NHC FCST.
THAT...IN TURN...WILL RESULT IN INCREASING LOW-LEVEL
CONVERGENCE...AS WELL AS GREATER MAGNITUDE AND AREAL COVERAGE OF
ENHANCED LOW-LEVEL VERTICAL SHEAR FAVORABLE FOR TORNADIC SUPERCELLS.
SHAPE/LENGTH OF FCST HODOGRAPHS CONTRIBUTES TO EFFECTIVE SRH
INCREASING TO 300-500 J/KG...AND NEARLY 90-DEG CRITICAL ANGLES
SUGGESTING FAVORABLE STREAMWISE VORTICITY. THIS WILL ENCOURAGE
PROGRESSIVELY MORE POTENTIAL FOR SUSTAINED ROTATION IN ANY
RELATIVELY DISCRETE UPDRAFTS.

3. RELATIVELY LARGE-THETA E AIR MASS -- NOW EVIDENT OFFSHORE SE FL
OVER WATERS OF GULF STREAM WHERE OCEAN HEAT CONTENT IS HIGH. THIS
AIR MASS SHOULD BE ADVECTED INLAND AMIDST INCREASING BOUNDARY-LAYER
WINDS TODAY...HELPING TO OFFSET MINOR OUTFLOW EFFECTS OF PASSING
CONVECTION. RESULTING MODIFICATIONS TO FCST SOUNDINGS YIELD
500-1000 J/KG MLCAPE AND LITTLE OR NO SBCINH.

4. POCKETS OF DIABATIC SFC HEATING MAY BOOST BUOYANCY LOCALLY EVEN
FURTHER...IN AREAS OF RELATIVE CLOUD-COVER BREAKS.

5. MULTIPLE ROUNDS OF AT LEAST LOOSELY BANDED CONVECTIVE MODE ARE
POSSIBLE AS CONVERGENCE INCREASES. THIS IS SUGGESTED BY STG
CONSENSUS OF HIGH-RES/CONVECTION-ALLOWING MODELS...AND SUPPORTS
INCREASING SUPERCELL/TORNADO CHANCES.

..EDWARDS/THOMPSON.. 08/26/2012

http://www.spc.noaa.gov/products/md/md1813.html

[wx247]

Here is a graphical representation of the areas now under a Tornado Watch until 5 p.m. from the SPC:

[jimboeh]

Still a lot of folks on the road in the Keys... Hope everyone stays safe.

[Sanibel]

Sunny when I woke-up at 10.

Have to hold my laptop down to keep it from blowing off my lap when NE gusts come into loft window. Will have to close window soon.

No rain.

Really glad I don't have to do direct hit preparations.

[ohiostorm]

Hey guys. Long time no see. I am now living in Orlando so I thought I would post a small report. Woke up this morning to overcast skies. We just had a small burst of rain come through. Little breezy, but nothing crazy.

[Umbris]

It's pretty quiet for the moment in NW Broward County though it was pretty rough with high wind and rain from the early morning til only a little while ago. Rain is picking up but the wind is still low. Everything here remains open and the only new closure is public transportation being canceled for the day.

[Hurricane Alexis]

I was expecting way more than occasional wind gusts....so far it's been an non-event.

[jlauderdal]

one feeder band flooded my street

[/URL]

[HurricaneFrances04]

Conditions aren't really surprising for a 65 mph tropical storm thats ~200 miles away. Squally weather with the occasional gusts. Marathon looks like its getting hammered right now.

[VeniceInlet]

Overcast and gusty here in Venice area, very hot and steamy outside. No rain yet but it is getting darker. Maybe gusts so far to 25 mph, I don't think we have had anything yet that could be considered a real feeder band. I am sure we'll get much more soon and thru at least Tues. I have one more pass thru the yard to secure breakables and then I'll be done.

My thoughts to those in the upper Gulf Coast, I can only imagine what they are going through now. I would try to get in the car and drive out of harm's way if you can.

[Sanibel]

Got to check my backed-up e-mails and get the porch cleared. Should miss by 150 miles west if it follows track. (Phew) Good for us, bad for those further north.

[gigabite]

one feeder band flooded my street

I was expecting Naples to get hammered yesterday by that pre-storm storm, but it just could not make it west of Everglades City. It looked masive. I didn't have time to check it out. I was busy getting Monday's work done. The wind has been picking up, and it just starter to rain here.

[cycloneye]

This damage occured in West Palm Beach.

[weatherSnoop]

Rain and small gusts finally hitting central Tampa

[VeniceInlet]

Still very little rain or wind in Venice.

[dizzyfish]

It appears that we (Pasco County) are out of the watches/warnings now.

[Sanibel]

Driven small drop tropical rain now with blustery gusts.

[scottw]

Tornado warning for Boyton beach area until 945pm

[fci]

Some of the strongest squalls yet occurring now in Lake Worth/Boynton.

[VeniceInlet]

Getting our first serious feeder band through in Venice. No lightning, just wind and rain.