[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 312342
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 PM EST SUN 31 OCT 2004

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

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...TROPICAL WAVES...

TROPICAL WAVE LOCATED OVER THE E CARIBBEAN ALONG 63W S OF 20N
MOVING W 10 KT. THE WAVE IS ENTANGLED WITHIN A BROAD FRONTAL
ZONE WHICH STRETCHES ACROSS AND JUST TO THE N OF THE ERN GREATER
ANTILLES...MAKING ITS EXACT LONGITUDE RATHER UNCERTAIN. THE AREA
ALSO LIES UNDER THE RIGHT ENTRANCE REGION OF A 50-60 KT UPPER
LEVEL JET WHICH EXTENDS NE OF PUERTO RICO AND THIS HAS HELPED TO
INDUCE CONVECTIVE ACTIVITY OVER A LARGE AREA SURROUNDING THE
WAVE. SCATTERED MODERATE CONVECTION IS FROM 12N-16N BETWEEN
65W-70W. SCATTERED MODERATE CONVECTION IS ALSO BECOMING MORE
WIDESPREAD FROM 17N-20N BETWEEN 60W-68W WITH VERY HEAVY RAINFALL
SPREADING OVER PUERTO RICO AND THE VIRGIN ISLANDS.

TROPICAL WAVE LOCATED OVER THE W CARIBBEAN AND CENTRAL AMERICA
NEAR 84W/85W S OF 20N MOVING W 5-10 KT. THE BROAD WAVE AXIS
EXTENDS FROM THE W TIP OF CUBA SWD ACROSS ERN HONDURAS AND
NICARAGUA WITH A LINE OF WIDELY SCATTERED MODERATE CONVECTION
FROM 11N-20N BETWEEN 81W-86W. HEAVY RAIN SQUALLS ARE POSSIBLE
OVER MOST OF CENTRAL AMERICA DURING THE NEXT 48 HRS AS THE WAVE
MOVES W...ESPECIALLY FROM HONDURAS SWD.

...ITCZ...

ITCZ AXIS IS ALONG 12N15W 9N20W 8N40W 12N55W 9N67W 9N79W 12N83W.
WIDELY SCATTERED MODERATE CONVECTION 30 NM N OF THE AXIS BETWEEN
19W-28W. SCATTERED MODERATE WITHIN 60 NM OF A LINE 4N20W 4N39W.
SCATTERED MODERATE/STRONG WITHIN 180 NM N AND 100 NM S OF THE
AXIS BETWEEN 37W-47W. SCATTERED SHOWERS/TSTMS WITHIN 120 NM OF
THE AXIS BETWEEN 53W-58W. SCATTERED MODERATE OVER NW VENEZUELA
AND N COLOMBIA. ISOLATED MODERATE OVER PANAMA AND THE SW
CARIBBEAN.

...DISCUSSION...

GULF OF MEXICO...
SURFACE PRESSURES HAVE BEGUN TO LOWER OVER THE WESTERN GULF OF
MEXICO AS A VIGOROUS FRONTAL SYSTEM PUSHES ACROSS THE ROCKY
MOUNTAINS AND SOUTHERN PLAINS STATES...BUT SATELLITE IMAGERY
STILL SHOWS NEARLY PERFECT CONDITIONS ACROSS THE AREA FOR NOW.
WITH THE SOUTHERLY RETURN FLOW CONTINUING TO INCREASE INTO E
TEXAS AND LOUISIANA...A FEW ISOLATED SHOWERS HAVE BEEN
DEVELOPING OVER THE NW GULF AND MOVING INLAND. HOWEVER...
ABUNDANT DRY AIR AND MODERATE/STRONG SUBSIDENCE COURTESY OF A
STRONG UPPER LEVEL HIGH OVER THE FLORIDA STRAITS IS PREVENTING
ANY DEEP CONVECTION FROM FORMING. THE COLD FRONT IS FORECAST TO
MOVE OFF THE TEXAS COAST EARLY TUESDAY...BUT SHOWERS/TSTMS WILL
BEGIN TO MOVE OFF THE COAST BEGINNING EARLY MONDAY...SPREADING E
TO FLORIDA THROUGH WEDNESDAY AND THURSDAY.

CARIBBEAN...
UNSETTLED WEATHER SPANS A GOOD CHUNK OF THE CARIBBEAN SEA THIS
EVENING AS A COUPLE OF TROPICAL WAVES MOVE ACROSS THE AREA AMONG
A DISSIPATING FRONTAL BOUNDARY NEAR PUERTO RICO AND THE NORTHER
LEEWARD ISLANDS. WATER VAPOR IMAGERY INDICATES MOIST UPPER LEVEL
WESTERLY FLOW COVERING MUCH OF THE AREA...BUT AN UPPER LOW IS
NOW DEVELOPING OFF THE S COAST OF THE DOMINICAN REPUBLIC AS DRY
AIR SURGES SWD ACROSS THE CNTRL CARIBBEAN. THIS DEVELOPING TROF
IS STRENGTHENING VERTICAL LIFT OVER THE E CARIBBEAN AND
PRODUCING AN ENVIRONMENT FAVORABLE FOR WIDESPREAD CONVECTION. IN
ADDITION...A 50-60 KT WLY JET EXTENDS NE OF PUERTO RICO AND
SYNOPTIC-SCALE LIFTING WITHIN THE RIGHT FRONT QUADRANT IS
ENHANCING CONVECTION NEAR PUERTO RICO AND THE VIRGIN ISLANDS. IT
IS ALSO INTERESTING TO NOTE THAT STRONG VERTICAL SHEAR EXTENDS
ACROSS THE ENTIRE LENGTH OF THE BASIN SINCE THE UPPER LEVEL
WESTERLY FLOW LIES ABOVE DEEPER LOW/MID-LEVEL EASTERLY FLOW.

SUBTROPICAL ATLANTIC...
THE UPPER LEVEL PATTERN IS BECOMING A LITTLE MORE PROGRESSIVE
OVER THE W ATLC AS RIDGING OVER THE SOUTHEAST U.S. AND GULF OF
MEXICO BEGINS TO SHIFT EWD. THE SFC RIDGE HAS ALSO SHIFTED TO
THE E WITH A 1022 MB HIGH CENTERED NEAR 30N63W AND A RIDGE
CONTINUING W ACROSS N/CNTRL FLORIDA. THE CENTRAL ATLC...IN THE
MEAN TIME...IS STILL BEING PLAGUED BY BROAD DEEP-LAYERED
TROUGHING. THE UPPER LEVEL AXIS IS NOW ALONG 42W AND IS
SUPPORTING THE SLOW EWD PROGRESSION OF A COLD FRONT ALONG 32N36W
26N46W...THEN AS A DISSIPATING STATIONARY FRONT TO 22N60W
19N69W. ASIDE FROM CONVECTION NEAR PUERTO RICO DESCRIBED IN THE
TROPICAL WAVE SECTION...WIDELY SCATTERED MODERATE CONVECTION IS
LOCATED UP TO 200 NM SE OF THE FRONT N OF 25N. TWO MORE COLD
SURGES ARE PULLING UP THE REAR BEHIND THE FRONT...WITH A SFC
TROF ALONG 30N44W 26N65W...AND A SECOND COLD FRONT APPROACHING
THE N BORDER OF THE AREA BETWEEN 45W-55W. FARTHER E...STRONG
UPPER LEVEL RIDGING IS CENTERED ALONG 22W OVER THE E ATLC AND
TRANSITIONS TO A DEEP TROF OVER NW AFRICA. A DISSIPATING
COLD/STATIONARY FRONTAL BOUNDARY HAS PUSHED WELL SW OF THE
CANARY ISLANDS ALONG 21N17W 26N26W 32N24W WITH STABLE
STRATOCUMULUS PUSHING S JUST OFF THE MOROCCAN COAST.

TROPICAL ATLANTIC...
BROAD UPPER LEVEL WESTERLIES ARE EJECTING OUT OF THE CARIBBEAN
OVER THE TROPICAL ATLC WATERS WITH ABUNDANT MOISTURE SPREADING
AS FAR E AS 40W. WEAK RIDGING IS ALIGNED ALONG 10N BUT CIMSS
SATELLITE-DERIVED WIND VECTORS INDICATE LESS RIDGING AND MORE
UPPER DIFFLUENCE...WHICH HAPPENS TO BE ENHANCING STRONG
CONVECTION ALONG THE ITCZ BETWEEN 37W-47W. FARTHER E...A NW/SE
TILTED SHORTWAVE TROF ALONG 20N39W 14N30W IS BEING UNDERCUT BY
THE WESTERLY FLOW TO THE W AND IS BEGINNING TO LIFT TO THE N.
THIS FEATURE HAS PRODUCED SOME DRYING TO ITS S AND HENCE
CONVECTIVE ACTIVITY ALONG THE ITCZ IN THIS AREA HAS BEEN MORE
LIMITED. ADDITIONAL DRY AIR STRETCHES OFF THE AFRICAN COAST TO
THE CAPE VERDE ISLANDS WITH STRONG RIDGING ALONG 20W STRETCHING
N INTO THE SUBTROPICS.

$$
BERG




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