[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 061801
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST THU DEC 06 2007

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN
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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 6N10W 5N30W 6N41W 2N51W. SCATTERED
MODERATE CONVECTION IS WITHIN 200 NM NORTH OF THE AXIS BETWEEN
32W-40W. WIDELY SCATTERED MODERATE CONVECTION IS WITHIN 150 NM
SOUTH OF AXIS EAST OF 20W TO THE AFRICAN COAST.
34W-42W.

DISCUSSION...

THE GULF OF MEXICO...
AS OF 1500 UTC...A FRONTAL SYSTEM EXTENDS EAST TO WEST ACROSS
THE NORTHERN GULF WATERS FROM JUST N OF TAMPA BAY TO THE DEEP
SOUTH IN TEXAS. THIS FRONT IS VERY DRY WITH LITTLE CLOUDS SEEN
ON SATELLITE PHOTOS NEAR THE BOUNDARY. HOWEVER...THERE IS SOME
CLOUDINESS ALONG THE MEXICAN COAST AND ALSO IN THE SE GULF NEAR
THE TAIL END OF A PREFRONTAL TROUGH. MOSAIC DOPPLER RADAR FROM
THE SE U.S. REVEALS A BAND OF SCATTERED SHOWERS AND TSTMS IN THE
STRAITS OF FLORIDA PUSHING TOWARD THE NW BAHAMAS. ISOLATED
SHOWERS ARE OVER PORTIONS OF S FLORIDA. A VERY WEAK SFC PRES
PATTERN REMAINS AHEAD OF THE FRONT RESULTING IN MAINLY LIGHT AND
VARIABLE WINDS ACROSS THE AREA. NLY WINDS OF 10 TO 15 KT ARE
FOUND BEHIND THE FRONT...PARTICULARLY OVER THE NE CORNER OF THE
GULF. THIS FRONT IS FORECAST TO MOVE NORTH OF THE AREA AS A WARM
FRONT TONIGHT. CURRENTLY...THE WEST PORTION OF THE FRONT HAS
BECOME NEARLY STATIONARY. IN THE MID AND UPPER LEVELS...A WELL
DEFINED CUT-OFF LOW IS SPINNING OVER NE MEXICO.  UPPER-LEVEL
SWLY WINDS TO THE E OF THE LOW ARE ADVECTING ABUNDANT MID/UPPER
LEVEL MOISTURE ACROSS MOST OF THE GULF.

THE CARIBBEAN SEA...
WEATHER CONDITIONS REMAIN PRETTY QUIET ACROSS THE BASIN THIS
AFTERNOON. VIS SAT IMAGERY SHOWS TYPICAL POCKETS OF LOW LEVEL
MOISTURE MOVING WWD UNDER AN ELY WIND FLOW. A WEAK SFC TROUGH IS
ANALYZED ACROSS THE MONA PASSAGE BASED ON SFC OBSERVATIONS AND
SATELLITE PICTURES. SCATTERED SHOWERS ARE FOUND ON THE NORTHERN
END OF THE TROUGH NEAR 21N66W. THE SAN JUAN DOPPLER RADAR
DEPICTS SCATTERED SHOWERS AND A FEW THUNDERSTORMS IN ASSOCIATION
WITH THIS TROUGH...WHICH IS EXPECTED TO MOVE WEST AND AWAY FROM
PUERTO RICO THIS AFTERNOON. THIS TROUGH WILL PROBABLY ENHANCE
THE SHOWER ACTIVITY OVER HISPANIOLA THIS AFTERNOON. LIKE THE
GULF OF MEXICO...WEAK SFC PRES PATTERN INDUCED BY THE SERIES OF
WEAK FRONTAL TROUGHS N OF THE AREA IS ALLOWING ELY TRADES TO BE
LIGHT ACROSS THE BASIN. ALOFT...A BROAD RIDGE COVERS THE
CARIBBEAN SEA ANCHORED ON A HIGH OVER NW VENEZUELA. SLY WINDS ON
THE WESTERN SIDE OF THE RIDGE ARE TRANSPORTING MID/UPPER-LEVEL
MOISTURE/HIGH CLOUDS FROM THE EPAC INTO THE SW CARIBBEAN THROUGH
CENTRAL AMERICA. THE RELAXED TRADE WIND FLOW IS NOT EXPECTED TO
LAST MUCH LONGER AS STRONG RIDGING BUILDS NE OF THE AREA. WINDS
ARE EXPECTED TO INCREASE TONIGHT.

THE ATLANTIC OCEAN...
A RATHER QUICK MOVING COLD FRONT HAS PUSHED OFF THE E COAST OF
THE U.S. EXTENDING FROM 31N70W THROUGH N-CENTRAL FLORIDA. THIS
FRONT IS FAIRLY WEAK AND DRY IN NATURE. A PREFRONTAL TROUGH...
POSSIBLY ASSOCIATED WITH AN OLD FRONTAL BOUNDARY RUNS FROM
27N76W ACROSS THE STRAITS OF FLORIDA TO 23N86W. LOW-LEVEL
CONVERGENCE ALONG THIS BOUNDARY IS PRODUCING SCATTERED SHOWERS
AND TSTMS ACROSS THE NW BAHAMAS...THE STRAITS OF FLORIDA AND THE
FLORIDA KEYS AND COASTAL WATERS. A SFC TROUGH EXTENDS FROM
29N50W TO 20N54W. THE WIND SHIFT ASSOCIATED WITH THIS TROUGH IS
WELL DEFINED ON AN EARLIER QUIKSCAT PASS. VIS SAT IMAGERY IS
STILL SHOWING A SWIRL OF LOW CLOUDS SPINNING OVER THE CENTRAL
ATLC NEAR 22N57W...MOVING WWD AHEAD OF THE ABOVE MENTIONED
TROUGH. ANOTHER SFC TROUGH IS OVER THE TROPICAL ATLC EXTENDING
FROM 21N42W TO 9N39W. SCATTERED MODERATE CONVECTION IS SEEN JUST
BEHIND THE TROUGH BETWEEN THE ITCZ AXIS AND 14N. SOME CYCLONIC
TURNING IS ALONG THE TROUGH AXIS NEAR 17N. A STRONG SFC RIDGE
DOMINATES THE EASTERN ATLC CENTERED ON A 1037 MB HIGH NEAR THE
AZORES. A DIFFERENCE IN PRES BETWEEN THIS HIGH AND THE TROUGH
OVER THE TROPICAL ATLC IS PRODUCING A LARGE AREA OF STRONG ELY
TRADES BETWEEN THE TROUGH AXIS AND THE WEST COAST OF AFRICA. THE
MID AND UPPER PATTERN IS QUITE AMPLIFIED CONSISTING OF A LARGE
ANTICYCLONE OVER THE AZORES AND A BROAD ELONGATED TROUGH TRAPPED
S OF THE HIGH. THE BROAD TROUGH HAS AN EMBEDDED UPPER LOW JUST
SW OF THE CAPE VERDE ISLANDS NEAR 24N24W. A JET STREAM BRANCH IS
ON THE S SIDE OF THE TROUGH. WV IMAGERY SHOWS A BAND OF
TRANSVERSE HIGH CLOUDS RELATED TO THIS FEATURE. UPPER DIFFLUENCE
BETWEEN THE UPPER LEVEL TROUGH AND AN UPPER HIGH LOCATED NEAR
5N45W IS HELPING TO INDUCE CONVECTION N OF THE ITCZ AND BEHIND
THE TROPICAL ATLC TROUGH. THE REMAINDER OF THE FORECAST AREA...
WEST OF 50W IS QUIET UNDER A FAIRLY UNIFORM ZONAL UPPER FLOW.

$$
GR



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