[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 071742
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST FRI DEC 07 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
1745 UTC

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 6N10W 3.5N25W 5N38W EQ50W. CLUSTERS
OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION ARE FROM THE
COAST OF SW AFRICA TO S OF THE EQUATOR E OF 12W TO ACROSS THE
PRIME MERIDIAN. CLUSTERS OF SCATTERED MODERATE CONVECTION ARE
FROM 2N-7N BETWEEN 17W-28W.

DISCUSSION...
GULF OF MEXICO...
HIGH PRES IS IN CONTROL OF THE WEATHER PATTERN ACROSS THE GULF
GIVING THE AREA PRETTY QUIET CONDITIONS AND SLY RETURN FLOW.
THE REMNANTS OF A FRONTAL BOUNDARY EXTENDING ACROSS THE N GULF
WATERS LIFTED N AND DISSIPATED. CURRENTLY...A SFC TROUGH IS
ANALYZED OVER SOUTHERN LOUISIANA. PATCHES OF LOW LEVEL MOISTURE
DOT THE REGION WITH A NARROW LINE OF SHOWERS AND ISOLATED TSTMS
ALONG 27N91W 26N94W. DOPPLER RADAR SHOWS SOME SHOWER ACTIVITY
OVER THE LOWER FLORIDA KEYS. ALOFT...A SHORTWAVE TROUGH EXTENDS
FROM SE LOUISIANA SW TO NEAR TAMPICO MEXICO. UPPER-LEVEL SWLY
FLOW TO THE EAST OF THE TROUGH ARE ADVECTING ABUNDANT MID/UPPER
LEVEL MOISTURE ACROSS THE GULF. AN UPPER-LEVEL RIDGE FROM THE
CARIBBEAN SEA EXTENDS NW INTO THE YUCATAN PENINSULA AND THE SE
GULF. PRES GRADIENT IS EXPECTED TO INCREASE OVER SE GULF AND
STRAITS OF FLORIDA LATE SATURDAY THROUGH MONDAY AS STRONG HIGH
PRES BUILDS ACROSS THE U.S. EASTERN SEABOARD/W ATLC.

CARIBBEAN SEA...
A WEAK SFC TROUGH EXTENDS FROM THE SE BAHAMAS ACROSS HAITI INTO
THE CARIBBEAN SEA. POCKETS OF LOW LEVEL MOISTURE ARE SEEN JUST
BEHIND THE TROUGH AXIS AFFECTING HISPANIOLA WITH MAINLY LIGHT
SHOWERS. PATCHES OF LOW LEVEL MOISTURE WITH EMBEDDED LIGHT
SHOWERS ARE ALSO SEEN OVER THE ABC ISLANDS AND NORTHERN
VENEZUELA. AFTER SEVERAL DAYS WITH A WEAK SURFACE PRESSURE
GRADIENT ACROSS THE AREA...WINDS ARE BEGINNING TO INCREASE OVER
THE EASTERN CARIBBEAN AS A TROUGH ALONG 50W APPROACHES THE
REGION AND SURFACE HIGH PRES BUILDS OVER W ATLC. THE NOAA WAVE
WATCH MODEL...NWW3...SHOWS NE TO E WINDS OF 20 TO 25 KT ACROSS A
GOOD PORTION OF THE BASIN...INCLUDING ALSO THE ANEGADA...MONA
AND WINDWARD PASSAGES. THESE WINDS WILL PERSIST DURING THE
UPCOMING WEEKEND. IN THE UPPER LEVELS...BROAD UPPER RIDGE
DOMINATES THE CARIBBEAN ANCHORED OVER SOUTH AMERICA AND EXTENDS
TO OVER THE GULF OF MEXICO AND THE W ATLC.

ATLANTIC OCEAN...
LOOKING AT THE BIG PICTURE FROM WEST TO EAST...A WEAK SURFACE
TROUGH EXTENDS OFF THE COAST OF THE CAROLINAS THROUGH 31N80W
ALONG THE FLORIDA COAST TO NEAR DAYTONA BEACH WITH LITTLE SHOWER
ACTIVITY. A COLD FRONT ENTERS THE AREA NEAR 31N57W THEN
CONTINUES SW TO NEAR 27N64W. A PRE-FRONTAL TROUGH IS WITHIN 200
NM AHEAD OF THE FRONT AND RUNS FROM 31N52W TO 24N58W. LOW-LEVEL
CONVERGENCE ALONG THIS TROUGH IS PRODUCING A 60 NM WIDE BAND OF
SCATTERED SHOWERS AND ISOLATED TSTMS. VIS SATELLITE IMAGERY
SHOWS A SWIRL OF LOW CLOUDS APPROACHING THE UK/US VIRGIN ISLANDS
AND PUERTO RICO. THIS FEATURE WILL AFFECT THOSE ISLANDS THIS
AFTERNOON AND THIS EVENING WITH ISOLATED TO SCATTERED SHOWERS. A
BROAD SFC TROUGH REMAINS OVER THE CENTRAL ATLC EXTENDING ALONG
49W/5OW FROM 14N-28N. THE WIND SHIFT ASSOCIATED WITH THIS TROUGH
IS WELL DEFINED ON AN EARLIER QUIKSCAT PASS AND SURFACE
OBSERVATIONS. SOME CYCLONIC TURNING IS SEEN ALONG THE TROUGH
AXIS NEAR 17N. THIS TROUGH HAS CLUSTERS OF MODERATE CONVECTION
JUST BEHIND THE AXIS BUT PARTICULARLY BETWEEN 17N-22N. THE GFS
COMPUTER MODEL HAS MOISTURE FROM THIS TROUGH SPREADING ACROSS
THE EASTERN CARIBBEAN DURING THIS WEEKEND. A STRONG SFC RIDGE
DOMINATES THE EASTERN ATLC CENTERED ON A 1038 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 24N28W. A JET STREAM
BRANCH WITH CORE WINDS OF 70-90 KT LIES ON THE S SIDE OF THE
TROUGH. WV IMAGERY SHOWS A BAND OF TRANSVERSE HIGH CLOUDS
ASSOCIATED WITH THIS FEATURE. THE REMAINDER OF THE FORECAST
AREA...WEST OF 50W IS UNDER A FAIRLY UNIFORM ZONAL UPPER FLOW.

$$
GR





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