[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 131124
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 AM EST WED DEC 13 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 1115 UTC.

...THE ITCZ...
ITCZ AXIS IS ALONG 6N11W 4N23W 4N40W 2N50W 1N55W. SCATTERED
MODERATE CONVECTION IS WITHIN 180 NM EITHER SIDE OF THE AXIS
BETWEEN 19W-36W. ISOLATED MODERATE IS WITHIN 150 NM S OF THE
AXIS E OF 15W.

...DISCUSSION...
THE GULF OF MEXICO...
THERE ARE A COUPLE WEAK FEATURES IN THE GULF PRODUCING AREAS OF
CLOUDINESS AND SOME SHOWER ACTIVITY. ONE IS A VERY WEAK
STATIONARY FRONTAL BOUNDARY FROM SRN LOUISIANA TO 27N94W. THIS
FRONT WAS PUSHED BACK TO THE W ON THE 06 UTC ANALYSIS TO BE IN
BETTER AGREEMENT WITH THE OBSERVED DEWPOINT GRAD WHICH IS ABOUT
10 DEG F OVER LAND AND BETWEEN 5-10 F OVER THE GULF WATERS. THE
PREVIOUS PLACEMENT OF THE FRONT IS NOW ANALYZED AS A SFC TROUGH
AS A CLEAR WIND SHIFT IS STILL NOTED IN THE BUOY OBS AHEAD OF
THE DEWPOINT GRAD ALONG 89W N OF 26N. SFC WINDS ARE BRIEFLY
TURNING NLY BEHIND THE FRONT BEFORE QUICKLY BECOMING RATHER
VARIABLE IN SE TEXAS. ASSOCIATED SHOWER ACTIVITY IS LOCATED IN
THE WARM SECTOR E OF THE WEAK FRONT. MOSAIC DOPPLER RADAR FROM
THE SE U.S. INDICATES THAT THE NARROW BANDS OF SHOWERS AND TSTMS
ACROSS THE FL PANHANDLE AND SE ALABAMA EARLIER THIS MORNING HAVE
DIMINISHED LEAVING ONLY ISOLATED TO SCATTERED SHOWERS ACROSS THE
ERN GULF...FLORIDA AND OTHER PORTIONS OF THE SE COAST. THE OTHER
WEAK FEATURE IS A SFC TROUGH WHICH RUNS FROM 25N87W SWD ACROSS
THE EXTREME NE PORTION OF THE YUCATAN PENINSULA AND INTO THE WRN
CARIB. FAIRLY WELL DEFINED BUT BROAD LOW-MID LEVEL CYCLONIC
TURNING IS NOTED ABOUT THE TROF AXIS. CONSIDERABLE CLOUDINESS
AND SCATTERED SHOWERS ARE WITHIN 240 NM E OF THE AXIS. LOOKING
AHEAD OVER THE NEXT COUPLE OF DAYS...THE WEAK FRONT WILL BEGIN
TO SLOWLY PROPAGATE E AS A SHORTWAVE TROF CURRENTLY OVER THE
SWRN U.S. APPROACHES THE AREA. GFS DRIFTS THE TROUGH IN THE SRN
GULF NWD AND DEVELOPS IT INTO A WEAK LOW AND THEN TRACKS IT
ACROSS FL. THERE IS MUCH UNCERTAINTY IN THIS SCENARIO AS THERE
IS NOT MUCH AGREEMENT IN THE MODELS.

THE CARIBBEAN SEA...
THERE IS SOME INSTABILITY IN THE WRN CARIB DUE TO A SFC TROUGH
WHICH EXTENDS FROM HONDURAS NWD ACROSS THE EXTREME NE YUCATAN
PENINSULA AND INTO THE SRN GULF. SFC OBS...SATELLITE IMAGERY
ALONG WITH LOW-LEVEL SAT DERIVED WINDS SHOW A BROAD AREA OF
CYCLONIC TURNING IN THE REGION. THERE IS EVEN SOME SIGNS OF A
SFC LOW DEVELOPING ALONG THIS TROUGH AS A SHIP OBS OFF THE COAST
OF BELIZE IS REPORTING A WEST WIND. SCATTERED SHOWERS AND
ISOLATED TSTMS APPEAR TO BE CONFINED TO WITHIN 200 NM E OF THE
TROUGH AXIS BASED ON CLOUD TOP TEMPS ON IR IMAGERY. GFS SHOWS
THIS FEATURE PULLING NWD AND CLOSING OFF LATER THIS WEEK. FOR
MORE DETAILS REFER TO THE GULF OF MEXICO SECTION ABOVE. ANOTHER
SFC TROUGH IS IN THE SW CARIB ANALYZED FROM 10N78W TO 16N83W.
THIS TROUGH HAS BECOME A LITTLE BETTER DEFINED WITH LOW-LEVEL
CYCLONIC TURNING IN THE WINDS EVIDENT IN SATELLITE IMAGERY AND
AN EARLIER QSCAT PASS. SOME LIFT NEAR THE SFC TROUGH ALONG WITH
WEAK UPPER DIFFLUENCE...BETWEEN A BROAD FLAT RIDGE CENTERED OVER
COLOMBIA AND STRONGER UPPER LEVEL WLY FLOW IN THE NW CARIB...IS
SPARKING SCATTERED SHOWERS AND ISOLATED TSTMS FROM 11N-17N
BETWEEN 78W-84W. DEEPER MORE CONVECTIVE ACTIVITY...ASSOCIATED
WITH THE ITCZ...LIES FURTHER S OVER COLOMBIA AND THE EXTREME SW
CARIB. THE REMAINDER OF THE AREA IS QUIET UNDER MODERATELY DRY
AIR ALOFT ASSOCIATED WITH THE BROAD UPPER LEVEL RIDGE. TRADE
WINDS ARE MOSTLY IN THE 15-20 KT RANGE EXCEPT FOR SOME STRONGER
WINDS IN THE S CENTRAL CARIB DUE TO LOWER PRES OVER N SOUTH
AMERICA. NO MAJOR CHANGES IN THESE WINDS ARE EXPECTED THRU THE
WEEK.

THE ATLANTIC OCEAN...
A LONGWAVE RIDGE/TROUGH/RIDGE PATTERN IS ESTABLISHED ACROSS THE
DISCUSSION AREA. VERTICALLY STACKED RIDGING EXISTS IN THE WRN
ATLC WITH THE MEAN AXIS ALONG 70W. A BAND OF STRONG MID-UPPER
LEVEL WINDS OR A WEAK JET STRETCHES FROM THE BAHAMAS EASTWARD TO
22N45W THEN RACING NWD IN RESPONSE TO THE TROUGH IN THE CENTRAL
ATLC. N OF THE WEAK JET...PLENTY OF DRY STABLE AIR ALOFT EXISTS
W OF 40W. THIS STRONG MID-LEVEL CAP IS KEEPING THE PATCHES OF
LOW-LEVEL MOISTURE DRIVEN BY FRESH NE-E WINDS SHALLOW. A BROAD
TROUGH DOMINATES THE CENTRAL ATLC WITH THE UPPER AXIS ALONG 43W.
AN ASSOCIATED COLD FRONT EXTENDS FROM 32N40W TO 20N50W. A PLUME
OF MOISTURE ASSOCIATED WITH THE SFC FRONT AND UPPER LEVEL JET
MENTIONED IS N OF 23N BETWEEN 35W-42W. A SECOND REINFORCING
FRONT REMAINS TO THE N OF THE AREA AND HAS BEGUN TO DISSIPATE.
THE WEAK SFC TROUGH THAT WAS LOCATED TO THE SE OF THE FRONT HAS
BEEN DROPPED FROM THE ANALYSIS AS THERE DOES NOT APPEAR TO BE A
PRECISE BOUNDARY. THE SUBTROPICAL E ATLC IS DOMINATED BY STRONG
VERTICALLY STACKED RIDGING WITH THE UPPER HIGH CENTER NEAR
31N23W AND THE 1030 MB SFC CENTER FURTHER TO THE NE. A WEAKENING
CUT OFF UPPER LEVEL LOW IS EMBEDDED IN THE LARGE SCALE RIDGE
NEAR 25N29W. THIS UPPER LEVEL FEATURE IS ONLY PRODUCING SOME
ISOLATED SHOWERS IN ITS VICINITY. THE UPPER LOW APPEARS THAT
IT WILL BE COMPLETELY OVERTAKEN SHORTLY BY A NARROW RIDGE TO ITS
W AS SUGGESTED BY GFS.

$$
CANGIALOSI




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