[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 251754
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST TUE DEC 24 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 5N20W 4N32W 3N44W EQUATOR AT
52W. SCATTERED MODERATE CONVECTION IS WITHIN 180 NM N OF THE
AXIS BETWEEN 31W-37W.

...DISCUSSION...

THE GULF OF MEXICO...
A WEAK RIDGE DOMINATES THE GULF THIS AFTERNOON GIVING THE AREA
LIGHT TO MODERATE WINDS. THE RETURN FLOW WILL INCREASE TONIGHT
OVER THE NW CORNER OF THE GULF AHEAD OF THE NEXT COLD FRONT THAT
WILL MOVE OFF THE TEXAS COAST WEDNESDAY AFTERNOON. A CUT-OFF LOW
OVER THE LOWER MISSISSIPPI VALLEY HAS A TROUGH OVER THE
NORTH-CENTRAL GULF WATERS. THE UPPER-LEVEL LOW WILL MOVE TOWARDS
THE CAROLINAS SUPPORTING THE DEVELOPMENT OF A SFC LOW ALONG A
FRONTAL BOUNDARY LOCATED JUST EAST OF NORTH-CENTRAL FLORIDA.
MOSAIC DOPPLER RADAR FROM THE SE U.S SHOWS BANDS OF SHOWERS WITH
EMBEDDED TSTMS AHEAD OF THE CUT-OFF LOW/TROUGH AFFECTING PARTS
OF GEORGIA AND ALABAMA AS WELL AS MISSISSIPPI AND THE FLORIDA
PANHANDLE. SCATTERED SHOWERS AND ISOLATED TSTMS ARE ALSO SEEN
ACROSS THE EAST COAST METRO AREAS OF FLORIDA AND THE ADJACENT
COASTAL WATERS. THIS ACTIVITY IS ASSOCIATED WITH THE ABOVE
MENTIONED FRONTAL BOUNDARY AND A WEAK INVERTED SURFACE TROUGH
EXTENDING ALONG 80W FROM 22N TO 27N. ANOTHER SFC TROUGH IS
ANALYZED ALONG 93W/94W SOUTH OF 23N. THIS TROUGH IS GENERATING
ISOLATED SHOWERS AND TSTMS OVER THE SW PORTION OF THE
GULF...INCLUDING THE BAY OF CAMPECHE. TROPICAL MOISTURE IS SEEN
STREAMING NORTHEASTWARD BY A JETSTREAM BRANCH FROM THE E PACIFIC
NE ACROSS THE CENTRAL GULF REACHING TO ACROSS THE SE UNITED
STATES. SATELLITE-DERIVED WINDS INDICATE A CORE WINDS OF 70-110
KT ASSOCIATED WITH THIS JETSTREAM.

THE CARIBBEAN SEA...
AMPLIFIED MID TO UPPER LEVEL RIDGING IS PRESENT OVER THE NW AND
CENTRAL SECTIONS OF THE SEA CREATING ABUNDANT MODERATE TO STRONG
SUBSIDENCE IN THESE AREAS. THE TAIL END OF A MID/UPPER LEVEL
TROUGH EXTENDS FROM THE E ATLC SW TO NEAR THE LEEWARD ISLANDS.
PRETTY QUIET CONDITIONS ARE FOUND ACROSS THE BASIN UNDER THE
INFLUENCE OF THIS STABLE ENVIRONMENT. TYPICAL PATCHES OF LOW
LEVEL CLOUDS WITH LIGHT RAIN SHOWERS ARE ACROSS THE AREA
PARTICULARLY OVER AND JUST SOUTH OF JAMAICA. LOW-LEVEL
CONVERGENCE COUPLED WITH A DIFFLUENT PATTERN ALOFT IS PRODUCING
A CLUSTER OF MODERATE TO ISOLATED STRONG CONVECTION OVER THE SW
CARIBBEAN. THIS CONVECTIVE ACTIVITY IS AFFECTING THE CARIBBEAN
PLAINS OF COSTA RICA AND PARTS OF PANAMA. A NARROW BAND OF
TRANSVERSE HIGH CLOUDS ASSOCIATED WITH A TROPICAL JETSTREAM IS
SEEN MOVING QUICKLY EASTWARD ACROSS THE SOUTHERN CARIBBEAN INTO
THE N TROPICAL ATLC. MODERATE EASTERLY WINDS WILL PERSIST OVER
THE AREA THIS AFTERNOON THROUGH SAT.

THE ATLANTIC OCEAN...
THIS REGION IS DOMINATED PRIMARILY BY TWO MAIN UPPER-LEVEL
FEATURES. THE FIRST ONE IS A BROAD RIDGE COVERING W OF ABOUT
55W. MODERATE TO STRONG SUBSIDENCE AND IMPLIED DRY/STABLE
AIRMASS IS FOUND WITHIN THE RIDGE AXIS. THE SECOND ONE IS A DEEP
LAYERED TROUGH THAT ENTERS THE AREA NEAR 31N41W AND EXTENDS TO
NEAR THE LEEWARD ISLANDS. AMPLE UPPER LEVEL MOISTURE IS EVIDENT
WITHIN 500 NM SE OF THE TROUGH. A CUT-OFF LOW IS DEVELOPING
ALONG THE TROUGH AXIS NEAR 29N42W. THE ATTENDANT FRONTAL SYSTEM
ENTERS THE AREA...AS A STATIONARY FRONT NEAR 31N37W THEN
CONTINUES TO 20N47W. THE SURFACE LOW PREVIOUSLY ANALYZED AS 1015
MB NEAR 23N51W BECAME DIFFUSED THIS MORNING...INSTEAD A SFC
TROUGH WAS ANALYZED ON THE 1200 UTC MAP ALONG 51W FROM 14N-20N.
A QUIKSCAT PASS FROM THIS MORNING ALSO CONFIRMED THAT THE LOW IS
NO LONGER DISCERNIBLE...BUT COMPUTER MODELS SUGGEST THAT A NEW
LOW MAY FORM ALONG THE FRONTAL BOUNDARY NEAR 28N40W. AN ASCAT
PASS FROM AROUND 1300 UTC SHOWS SOME CYCLONIC CIRCULATION IN
THIS AREA. TIGHT PRES GRADIENT BETWEEN THIS FRONT AND THE RIDGE
TO THE W OF THE FRONT IS PRODUCING GALE FORCE WINDS FROM 23N TO
28N BETWEEN 40W AND 60W. AS A RESULT...A GALE WARNING HAS BEEN
POSTED. POCKETS OF LOW LEVEL MOISTURE ARE SEEN ACROSS THE
BAHAMAS AND THE STRAITS OF FLORIDA MOVING NW UNDER A PREVAILING
SE WIND FLOW AROUND THE SOUTHERN PERIPHERY OF A SFC RIDGE
EXTENDING INTO THE AREA BETWEEN THE PREVIOUSLY MENTIONED FRONTAL
BOUNDARIES. RIDGING ALSO DOMINATES THE E ATLC ANCHORED ON A 1029
HIGH LOCATED JUST WEST OF THE MADEIRA ISLANDS. THE UPPER FLOW IS
GENERALLY ZONAL OVER THE TROPICAL ATLC TO THE E AND SE OF THE
FRONT/TROUGH. HIGH LEVEL MOISTURE STREAMING EASTWARD IS LOCATED
S OF 18N...REACHING THE CAPE VERDE ISLANDS.

$$
GR




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