Severe Thunderstorm Warning 209, NWS Jacksonville, FL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSONVILLE FL
230 PM EDT SAT AUG 18 2001

CURRENT...CONVECTION HAD DEVELOPED ALONG A SHEAR LINE OVER THE BIG
BEND AND IS MOVING EAST ACROSS THE WESTERN PORTIONS OF THE FORECAST
AREA (FA)...MAINLY THE SUWANNEE VALLEY. CUMULUS CLOUD STREETS WERE
NOTED ON VISIBLE IMAGERY OVER THE BALANCE OF THE FA EMBEDDED IN THE
ANTI-CYCLONIC LOW LEVEL FLOW AROUND THE RIDGE AXIS.

MODELS...ALL OF THE MODELS ARE IN GOOD AGREEMENT WITH A BROAD UPPER
LEVEL TROF DIGGING SOUTHWARD INTO THE LOWER MISSISSIPPI RIVER
VALLEY TONIGHT AND SUN. THIS DRIVES THE FIRST COLD FRONT...CURRENTLY
OVER NORTHERN GA...TO SOUTHEASTERN GEORGIA ON SUNDAY WHERE IT
STACKS UP AGAINST A SOUTHWESTWARD EXTENSION OF THE BERMUDA-AZORES
RIDGE OVER CENTRAL FL. A SECOND FRONT MOVES DOWN ON MONDAY...BUT IT
ONLY LOOKS LIKE IT WILL PENETRATE TO NORTH FLORIDA. OVERALL AVN MODEL
NUMERAL GUIDANCE IS PREFERRED WITH A MERGER BETWEEN THE MESO-ETA AND
AVN MODELS THE BEST SOLUTION.

TONIGHT...CONVECTION MAY CONTINUE LONGER OVER SOUTHEAST GA AND THE
SUWANNEE VALLEY DUE TO THE FOCUSING OF THE FRONTAL SYSTEM MOVING
SOUTH AND A LOW LEVEL MOISTURE FEED FROM APALACHEE BAY. WILL GO WITH
SOME CONVECTION POSSIBLE ALL NIGHT IN THOSE AREAS WITH EVENING POPS
ELSEWHERE. THE EVENING CAN CLEAN IT UP IF THIS DOESNT PAN OUT.

SUN/SUN NIGHT...LOOKS LIKE THE HIGHEST POPS WILL REMAIN ALONG THE
STATE LINE DURING THE DAY WITH ANOTHER SHOT OF DEEP LEVEL MOISTURE
ENTERING SOUTHEAST GA SUN NIGHT. WILL KEEP A CHANCE OF POPS IN THE
FORECAST FOR GA BOTH PERIODS. MORE DIURNAL CONVECTION OVER N FL
WITH A WEAK EAST COAST SEA BREEZE DUE TO THE LOW LEVEL SOUTHWESTERLY
FLOW AROUND THE RIDGE AXIS.

MON/MON NIGHT...DITTOS TO THE ABOVE DISCUSSION WITH LESS MOISTURE
AVAILABLE OVER SOUTHEAST GA OVERNIGHT.

EXTENDED...THOSE LOOKING AT THE EXTENDED MODELS NO DOUBT HAVE NOTED
THAT THE AVN MEX MODEL GUIDANCE INDICATES A SOLUTION WHICH BRINGS
CHANTAL INTO THE CENTRAL GULF OF MEXICO ON TUE-WED WITH THE DEEP
LEVEL MOISTURE SHEARED NORTHEAST OVER THE REGION. REALLY THESE
MOISTURE FIELDS LOOK MORE LIKE A WINTERTIME NORTHEASTER THAN A
TROPICAL CYCLONE WITH A DRY SLOT AND EVERYTHING...CALLING THEM INTO
QUESTION. MORE PLAUSIBLE SCENARIOS ARE THE NOGAPS & UKMET SOLUTIONS
WHICH TAKE IT WEST WITHOUT EVER EFFECTING THE FA (EVEN WITH ENHANCED
MOISTURE). SO...GIVEN THE NOON MEDIUM RANGE CONFERENCE CALL AND THE
CURRENT UNCERTAINTIES HIGHLIGHTED IN THE NHC DISCUSSION...WILL GO
WITH THE IDEA THAT THE SYSTEM CONTINUES MOVING WEST-NORTHWEST...WELL
AWAY...FROM THE REGION. WITH THAT IN MIND WILL CONTINUE WITH A
DIURNAL CONVECTIVE CYCLE ACROSS THE FA WITH THE RIDGE HOLDING SWAY.

MARINE...WE CONTINUE TO SEE A 3 FOOT SWELL WITH A 10 SECOND
PERIOD AT GRAYS REEF AND R2 TOWER. MODELS CONTINUE TO EXHIBIT A
NOCTURNAL SURGE OVERNIGHT AND I LIKE THE CURRENT HANDLING IN THE
MARINE FORECAST. OVERALL WILL KEEP WINDS AND SEAS BELOW SMALL CRAFT
EXERCISE CAUTION CRITERIA.

PRELIM

AMG 75/92/73/90 2525
SSI 78/91/77/87 2525
JAX 76/93/75/92 2525
GNV 74/91/74/90 2424 05

.JAX...
.GA...NONE.
.FL...NONE.

SANDRIK