[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 141112
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 AM EST THU DEC 14 2006

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...
CENTRAL AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...
NORTHEASTERN SECTIONS OF SOUTH AMERICA...AND THE ATLANTIC
OCEAN TO THE AFRICAN COAST FROM THE EQUATOR TO 32N.
THE FOLLOWING INFORMATION IS BASED ON SATELLITE IMAGERY...
METEOROLOGICAL ANALYSIS...WEATHER OBSERVATIONS...AND RADAR.

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1100 UTC.

...THE ITCZ...
ITCZ AXIS IS ALONG 7N11W 4N22W 3N39W EQ50W. SCATTERED MODERATE
CONVECTION IS WITHIN 120 NM N AND 180 NM S OF THE AXIS BETWEEN
20W-32W AND WITHIN 240 NM N BETWEEN 32W-40W. ISOLATED MODERATE
IS WITHIN 120 NM S OF THE AXIS E OF 20W.

...DISCUSSION...
THE GULF OF MEXICO...
A SFC TROUGH REMAINS NEARLY STATIONARY IN THE SRN GULF ALONG
86W/87W S OF 26N EXTENDING INTO THE WRN CARIB. RATHER DISTINCT
LOW-LEVEL CYCLONIC TURNING IS NOTED IN SFC OBS...SATELLITE
IMAGES AND SAT LOW-LEVEL DERIVED WINDS MAKING THE AXIS OF THE
TROUGH EASY TO LOCATE. SCATTERED SHOWERS AND TSTMS ARE LOCATED
TO THE E OF THE TROUGH AXIS TO 82W. THE ERN HALF OF THIS
MOISTURE SWATH IS SHOWING UP ON THE KEY WEST AND TAMPA BAY
88-D'S WHICH DEPICT A FEW MODERATE ECHOES OFFSHORE. HOWEVER MOST
OF THEM APPEAR TO BE LOSING SOME STEAM AS THEY HEAD TOWARDS THE
COAST. SWIFT UPPER LEVEL WESTERLIES IS SHEARING THIS ACTIVITY
AND SPREADING DEBRIS SHOWERS ACROSS SOUTH AND CENTRAL FLORIDA
BETWEEN LAKE OKEECHOBEE AND ORLANDO. THE UPPER LEVEL FLOW IS A
RATHER UNIFORM W-SWLY ACROSS THE ENTIRE AREA AHEAD OF AN
APPROACHING SHORTWAVE TROUGH LOCATED ABOVE TEXAS AND NRN MEXICO.
A PLUME OF HIGH LEVEL MOISTURE...ASSOCIATED WITH THE SUBTROPICAL
JET ORIGINATING AT THE BASE OF THE TROUGH...IS BEING ADVECTED
FROM THE EPAC ACROSS NRN MEXICO AND INTO THE NRN GULF. AS THIS
TROUGH APPROACHES IT WILL SPREAD THIS UPPER LEVEL CLOUDINESS
EASTWARD AND WILL LIKELY STEER THE SFC TROUGH IN THE SRN GULF
NORTHEASTWARD ACROSS FLORIDA ON FRI. ONCE THE TROUGH MOVES OUT
WEAK TO MODERATE HIGH PRES WILL BUILD IN.

THE CARIBBEAN SEA...
THERE ARE TWO WEAK SFC TROUGHS ANALYZED IN THE WRN CARIB. ONE OF
THESE IS IN THE NW PART OF THE AREA ALONG 87W N OF 18N EXTENDING
INTO THE SRN GULF. MOST OF THE ASSOCIATED SHOWER ACTIVITY IS N
OF THE AREA BUT ISOLATED SHOWERS ARE LIKELY OCCURRING ACROSS THE
YUCATAN PENINSULA. THE OTHER IS IN THE SW PORTION ANALYZED FROM
9N79W TO 16N83W. WHILE THIS AREA TYPICALLY HAS A CLIMATOLOGICAL
VEERING IN THE WINDS OR TROUGH FEATURE...THE LOW-LEVEL TURNING
TODAY IS A LITTLE MORE PRONOUNCED THAN USUAL SO IT REMAINS
ANALYZED AS A SYNOPTIC WEATHER FEATURE. SOME SFC LIFT NEAR THE
WEAK BOUNDARY ALONG WITH WEAK UPPER DIFFLUENCE...BETWEEN AN
UPPER HIGH CENTERED OVER NICARAGUA AND STRONGER UPPER LEVEL WLY
FLOW IN THE NW CARIB...IS SPARKING SCATTERED SHOWERS AND
ISOLATED TSTMS FROM 12N-17N BETWEEN 81W-85W AND FURTHER S CLOSER
TO THE ITCZ AXIS S OF 11N BETWEEN 78W-85W. THE REMAINDER OF THE
AREA IS QUIET UNDER MODERATE DRY AIR ALOFT AND NW-WLY UPPER
LEVEL FLOW. TRADE WINDS ARE MOSTLY IN THE 15-20 KT RANGE AND
LITTLE CHANGE IS EXPECTED THRU FRI AS THE SFC RIDGE REMAINS TO
THE NE OF THE REGION.

SUBTROPICAL ATLANTIC...
A RIDGE/TROUGH/RIDGE PATTERN IS ESTABLISHED ACROSS THE
SUBTROPICAL ATLC. HIGHLY TILTED STACKED RIDGING EXISTS IN THE
WRN ATLC WITH THE MEAN UPPER LEVEL AXIS EXTENDING FROM CUBA
NEWARD TO BERMUDA. THE SFC HIGH IS LOCATED WELL TO THE N OF THE
AREA. THE PRES GRAD BETWEEN THIS HIGH AND LOW PRES TO THE E IS
SETTING UP A REGION OF 20-30 KT WINDS N OF 18N BETWEEN 35W-60W.
FOR DETAILS ON THE WINDS AND SEAS REFER TO THE HIGH SEAS
FORECAST ...MIAHSFAT2. A WEAK SFC TROUGH IS LOCATED N OF THE
MONA PASSAGE ALONG 66W/67W FROM 19N-24N POSSIBLY PRODUCING
ISOLATED SHOWERS AND TIGHTENING THE PRES GRAD SLIGHTLY. PLENTY
OF DRY STABLE AIR ALOFT EXISTS BETWEEN 35W-70W PROVIDING A
STRONG MID-LEVEL CAP WHICH IS KEEPING THE PATCHES OF LOW-LEVEL
MOISTURE SHALLOW. A BROAD TROUGH DOMINATES THE CENTRAL ATLC WITH
THE UPPER AXIS ALONG 39W. AN ASSOCIATED OLD FRONTAL BOUNDARY
EXTENDS FROM A 1011 MB LOW NEAR 33N32W SW TO A NEWLY FORMED 1011
MB LOW NEAR 28N36W CONTINUING TO 17N40W. MULTILAYERED CLOUDS AND
EMBEDDED ISOLATED SHOWERS ARE LOCATED MAINLY WITHIN 180 NM E OF
THE TROUGH AXIS. THE DEEPEST MOISTURE IS N OF THE AREA WHERE
STRONG UPPER LEVEL WINDS ARE PROVIDING MORE SUPPORT FOR
UNSETTLED WEATHER. THE E ATLC IS DOMINATED BY AN UPPER RIDGE
WITH THE MAIN HIGH CENTER NEAR 29N21W. HOWEVER THIS RIDGE IS
BECOMING SQUASHED BETWEEN THE TROUGH IN THE CENTRAL ATLC AND A
VERY LARGE CUT OFF IN THE SRN MEDITERRANEAN SEA.

TROPICAL ATLANTIC...
NEARLY ZONAL UPPER LEVEL FLOW ON THE N SIDE OF A BROAD FLAT
RIDGE COVERS MUCH OF THE TROPICAL ATLC. WATER VAPOR IMAGERY
INDICATES A FAIR AMOUNT OF MODERATE DRY AIR ALOFT ABOVE THE AREA
PROVIDING A FAIRLY STABLE ENVIRONMENT LIMITING CONVECTION TO THE
ITCZ. A WEAK SFC TROUGH IS LOCATED ALONG 50W FROM 12N-16N
PRODUCING ONLY BROKEN LOW CLOUDS...ISOLATED SHALLOW SHOWERS AND
A SLIGHT WIND SHIFT WITHIN 180 NM OF ITS AXIS.

$$
CANGIALOSI



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