[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 302325
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SUN SEP 30 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...SPECIAL FEATURE...

STRONG SHEAR HAS TAKEN ITS TOLL ON TROPICAL DEPRESSION MELISSA
AND THE FINAL ADVISORY HAS BEEN ISSUED. ONLY VERY SMALL SHORT
LIVED BURSTS OF CONVECTION ARE ASSOCIATED WITH THE SYSTEM.
CURRENTLY...SCATTERED MODERATE IS FROM 16N-17N BETWEEN 33W-35W.
AS OF 30/21Z...THE WEAKENING SYSTEM WAS CENTERED NEAR 16.3N
34.0W OR ABOUT 575 NM WEST OF THE CAPE VERDE ISLANDS...MOVING
WNW AT 12 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1007 MB.
MAXIMUM SUSTAINED WIND SPEED IS 25 KT WITH GUSTS TO 35 KT. SEE
LATEST NHC FORECAST ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT4/WTNT24 KNHC AND THE PUBLIC ADVISORY UNDER
MIATCPAT4/WTNT34 KNHC FOR MORE DETAILS.

...TROPICAL WAVES...

TROPICAL WAVE LIES ACROSS THE SRN CAPE VERDE ISLANDS ALONG 24W S
OF 15N MOVING W 15 KT OVER THE PAST 24 HOURS. THIS LOW AMPLITUDE
WAVE HAS BECOME A LITTLE LESS DEFINED SINCE MOVING OFF THE
AFRICAN COAST A DAY OR SO AGO. NIGHT CHANNEL VIS IMAGERY AND
DERIVED WINDS SHOW A RATHER NARROW NW-SE TITLED AREA OF LOW TO
MID LEVEL TURNING IN THE ASSOCIATED CLOUDINESS. CONVECTIVE
ACTIVITY IS MINIMAL...ONLY ISOLATED SHOWERS AND TSTMS ARE WITHIN
180 NM OF THE AXIS.

TROPICAL WAVE IS ALONG 41W S OF 14N MOVING W 10 KT. THIS WEAK
WAVE IS BARELY IDENTIFIABLE ON SATELLITE IMAGERY DUE TO THE
LACK OF ANY ORGANIZED CLOUDINESS. THE MIMIC TPW ANIMATION DOES
REVEAL A SLIGHT MOISTURE BULGE MOVING W...LIKELY ASSOCIATED
WITH THIS WEAK WAVE.

THE NRN PORTION OF A TROPICAL WAVE ALONG 89W EXTENDS ACROSS
CENTRAL AMERICA. THERE IS A CONSIDERABLE AREA OF DISORGANIZED
CLOUDINESS...SHOWERS AND TSTMS ENHANCED BY THIS LOW-LEVEL
FEATURE. HOWEVER...BASED ON THE STRUCTURE AND OVERALL LITTLE
MOVEMENT SINCE YESTERDAY DIFFLUENCE ALOFT IS LIKELY THE PRIMARY
CULPRIT. MORE ON THIS ACTIVITY IN THE CARIBBEAN DISCUSSION
BELOW.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 6N11W 5N26W 8N39W 9N60W. BESIDES FOR
THE ACTIVITY ASSOCIATED WITH THE TROPICAL WAVES...SCATTERED
SHOWERS AND TSTMS ARE WITHIN 360 NM S OF THE AXIS BETWEEN
20W-40W. A CLUSTER OF MODERATE CONVECTION IS ALONG AND JUST OFF
THE AFRICAN COAST FROM 10N-12N E OF 17W.

DISCUSSION...

GULF OF MEXICO...
RATHER STRONG NELY WINDS...15-25 KT...IS OBSERVED ACROSS THE E
GULF. THIS STRONG FLOW IS ASSOCIATED WITH A TIGHT PRES PATTERN
SET UP BETWEEN A VERY HEALTHY 1035 MB HIGH OFF THE NRN NEW
ENGLAND COAST AND A STALLED FRONT WHICH EXTENDS FAR TO THE S
OVER NW CUBA. BUOY DATA IN THE REGION SHOWS AN INCREASE IN SEA
HEIGHTS WITH A FEW REPORTING 8 FT. BESIDES FOR THE STRONG
WINDS...THE WEATHER IS RATHER TRANQUIL WITH ONLY SCATTERED LOW
TO MID LEVEL CLOUDS ACROSS THE REGION. THIS FAIR WEATHER IS
BEING PRODUCED BY LARGE SCALE STRONG SUBSIDENCE E OF 95W ON THE
BACK SIDE OF AN UPPER LOW CENTERED JUST W OF FT MYERS FLORIDA.
ONE EXCEPTION IN THE WIDESPREAD FAIR WEATHER IS OVER THE EXTREME
SE PORTION WHERE MOSAIC DOPPLER RADAR SHOWS SCATTERED SHOWERS
AND TSTMS PRESSING SW ACROSS SE FLORIDA...THE KEYS AND INTO THE
STRAITS. FOR DETAILS ON THIS ACTIVITY REFER TO THE ATLANTIC
DISCUSSION BELOW. FARTHER W...AN UPPER RIDGE IS CENTERED OVER
CENTRAL MEXICO PRODUCING SOME HIGH CLOUDINESS ACROSS THE REGION
W OF 95W.

CARIBBEAN SEA...
SHOWERS AND TSTMS ARE AFFECTING A GOOD PORTION OF THE CARIBBEAN
SEA THIS EVENING. STARTING IN THE W CARIB...THE MAIN TRIGGERS
ARE A TROPICAL WAVE LOCATED OVER CENTRAL AMERICA AND A DIFFLUENT
PATTERN BETWEEN WLY FLOW ON THE S SIDE OF AN UPPER LOW AND ELY
FLOW ON THE SW PERIPHERY OF A RIDGE OVER MEXICO. THIS
INSTABILITY AND LIFT IS PRODUCING DISORGANIZED SCATTERED SHOWERS
AND TSTMS S OF 18N W OF 78W. A SEPARATE AREA OF SIMILAR ACTIVITY
LIES OVER THE CENTRAL CARIB N OF 16N BETWEEN 70W-77W. THE
FORCING HERE IS CONVERGENCE NEAR THE BASE OF A SW ATLC LOW-LEVEL
TROUGH AND AGAIN DIFFLUENCE ALOFT BETWEEN THE UPPER LOW IN THE
SE GULF AND A TITLED UPPER RIDGE WHICH RUNS FROM COLOMBIA ACROSS
HISPANIOLA. SHOWERS AND TSTMS ARE MORE ISOLATED IN COVERAGE
ACROSS THE E CARIB ROUGHLY E OF 66W. THIS LESS ORGANIZED
ACTIVITY IS ASSOCIATED WITH DEBRIS CLOUDINESS SPREAD OVER FROM
THE CENTRAL CARIB AND THEN LIFTED BY THE DEEP LAYERED LOW PRES
SYSTEM...REMNANTS OF KAREN...JUST E OF THE AREA. MORE ON THIS
SYSTEM IN THE ATLANTIC DISCUSSION BELOW. CLUSTERS OF MODERATE TO
STRONG ITCZ RELATED CONVECTION HAVE FORMED THIS AFTERNOON OVER
PORTIONS OF NRN VENEZUELA AND COLOMBIA.

ATLANTIC OCEAN...
THERE ARE A FEW AREAS THAT WE ARE MONITORING IN THE ATLANTIC
DISCUSSION AREA...BUT OVERALL IT HAS QUIETED DOWN SOME AS KAREN
AND NOW MELISSA ARE NO LONGER TROPICAL CYCLONES. IN THE SW
ATLC...THERE IS A MESSY SFC PATTERN. THE FOCUS IS A WEAK AREA OF
LOW PRES...ANALYZED 1010 MB BASED ON OBS IN THE BAHAMAS
...CENTERED NEAR 26N74W. A TROUGH HANGS SSW FROM THE LOW ACROSS
THE CENTRAL BAHAMAS AND ERN CUBA. A STALLED SLOWLY WEAKENING
FRONTAL BOUNDARY LIES JUST TO THE W OF THE LOW ALONG 32N65W
25N77W TO THE WRN TIP OF CUBA. CONVERGENCE ALONG THESE
BOUNDARIES COUPLED WITH DIFFLUENCE ALOFT BETWEEN AN UPPER LOW
OVER THE SE GULF AND AN UPPER RIDGE ALONG 67W/68W IS PRODUCING
SCATTERED SHOWERS AND TSTMS BETWEEN 67W-75W. IR IMAGERY SHOWS A
MID-LEVEL LOW BEGINNING TO TAKE SHAPE TO THE W OF THE FRONTAL
ZONE NEAR 26N78W. DOPPLER RADAR FROM MIAMI SHOWS SWATHS OF
SHOWERS AND TSTMS PRESSING SW ON THE BACK SIDE OF THAT ENERGY.
IN ADDITION TO THE HEAVY RAIN THREAT...STRONG NELY WINDS ARE
PROBABLY THE BIGGEST CONCERN WITH SFC DATA AND QSCAT SUGGESTING
WINDS TO 30 KT. THESE LOCAL WINDS ALONG WITH A LARGE NELY FETCH
IS PRODUCING DANGEROUS MARINE CONDITIONS WITH SEAS IN THE 10-15
FT RANGE.

IN THE TROPICAL CENTRAL ATLC...A LARGE AREA OF SCATTERED SHOWERS
AND ISOLATED TSTMS ARE ASSOCIATED WITH THE REMNANTS OF KAREN
WHICH IS CENTERED NEAR 16N58W...ESTIMATED TO BE 1011 MB. THE
ILL-DEFINED LOW LEVEL CIRCULATION IS LOCATED TO THE SE OF AN
UPPER LOW WHICH IS PROVIDING STRONG W TO SWLY SHEAR OVER THE
REMNANT TC. MOST OF THE SHOWER ACTIVITY IS DOWNSHEAR AND IN A
DIFFLUENT ZONE TO THE E OF THE REMNANTS FROM 13N-19N BETWEEN
52W-60W. SHALLOWER ACTIVITY HAS SPREAD W OF THE LOW OVER THE
LEEWARD ISLANDS...STEERED BY THE LOW-LEVEL FLOW.

THE E ATLC IS RELATIVELY QUIET BESIDES FOR THE SMALL BURSTS OF
CONVECTION NEAR WHATS LEFT OF MELISSA. FOR DETAILS ON THIS
WEAKENING SYSTEM REFER TO THE SPECIAL FEATURES SECTION ABOVE.
THE PATTERN ACROSS THE E ATLC CONSISTS OF LARGE SCALE TROUGHING
IN THE SUBTROPICS AND RIDGING IN THE TROPICS. THE TROUGHING IS
ASSOCIATED WITH A VERY LARGE NEARLY STATIONARY OCCLUDED LOW
CENTERED W OF THE IBERIAN PENINSULA. ITS ASSOCIATED COLD FRONT
ACTUALLY EXTENDS INTO OUR AREA ACROSS THE AZORES ALONG 32N16W
30N27W 31N38W. ISOLATED SHOWERS ARE POSSIBLE WITHIN 60 NM AHEAD
OF THE FRONT.

$$
CANGIALOSI







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