[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 161750
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU OCT 16 2008

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF
SOUTH AMERICA...AND 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.

...SPECIAL FEATURES...
HURRICANE OMAR IS QUICKLY WEAKENING AS IT MOVES RAPIDLY AWAY
FROM THE NORTHERN LEEWARD ISLANDS. HEAVY RAINFALL THREAT REMAINS
FOR THE NORTHERN AND CENTRAL LESSER ANTILLES. AT 16/1500 UTC...
OMAR IS CENTERED NEAR 20.2N 61.3W OR ABOUT 155 NM...290 KM...
NORTHEAST OF THE NORTHERN LEEWARD ISLANDS MOVING NE OR 035 DEG
AT 20 KT. THIS GENERAL MOTION IS EXPECTED DURING THE NEXT TWO
DAYS. ESTIMATED MINIMUM CENTRAL PRESSURE IS 980 MB. MAXIMUM
SUSTAINED WIND SPEED HAS DECREASED TO 75 KT WITH GUSTS TO 90 KT.
PLEASE SEE LATEST NHC PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS
MIATCPAT5/WTNT35 KNHC AND THE FULL FORECAST/ADVISORY UNDER
AWIPS/WMO HEADERS MIATCMAT5/WTNT25 KNHC FOR MORE DETAILS. OMAR
REACHED NEAR THE THRESHOLD OF CATEGORY 4 EARLY THIS MORNING
AROUND 06Z. A FEW HOURS LATER...VISIBLE SATELLITE IMAGERY
REVEALED AN EXPOSED LOW-LEVEL CENTER INDICATING A RAPIDLY
WEAKENING TREND OF THIS CYCLONE. BANDS OF MODERATE TO ISOLATED
STRONG CONVECTION...ASSOCIATED WITH THE OVERALL CIRCULATION OF
OMAR...CONTINUES TO AFFECT THE NORTHERN AND CENTRAL LESSER
ANTILLES AND THE FAR EASTERN CARIBBEAN SEA MAINLY E OF 64W. ST.
THOMAS REPORTED THIS MORNING 2.42 INCHES OF RAIN IN 24 HOURS.

...TROPICAL WAVES...
A TROPICAL WAVE IS MOVING ACROSS THE CAPE VERDE ISLANDS. ITS
AXIS IS ALONG 23W/24W S OF 18N MOVING W NEAR 10-15 KT. CYCLONIC
CURVATURE IS EVIDENT ON SATELLITE IMAGERY WITH CLUSTERS OF
SCATTERED MODERATE/ISOLATED STRONG CONVECTION MAINLY BEHIND THE
WAVE AXIS FROM 11N-15N AND BETWEEN 22W-25W.

AN ACTIVE TROPICAL WAVE IS ALONG 45W S OF 14N MOVING W NEAR 10
KT. THE WAVE SHOWS A CLASSIC INVERTED-V PATTERN ON SATELLITE
IMAGERY WITH SCATTERED TO NUMEROUS MODERATE TO ISOLATED STRONG
CONVECTION WITHIN 180-200 NM EITHER SIDE OF THE WAVE AXIS FROM
8N-12N.

...THE ITCZ...
THE ITCZ IS PRETTY ACTIVE TODAY. ITS AXIS IS CENTERED ALONG
8N13W 6N30W 8N42W 6N50W 9N61W. IN ADDITION TO CONVECTION
ASSOCIATED WITH THE TROPICAL WAVES...SCATTERED MODERATE/ISOLATED
STRONG CONVECTION IS WITHIN 125 NM N OF AXIS BETWEEN 25W-41W.
SIMILAR CONVECTION IS WITHIN 100 NM SOUTH OF AXIS BETWEEN
35W-41W.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER-LEVEL LOW REMAINS INLAND OVER NORTH-CENTRAL MEXICO NEAR
24N100W. AN BROAD UPPER-LEVEL RIDGE ANCHORED ON A HIGH JUST N OF
THE YUCATAN PENINSULA COVERS MOST OF THE GULF REGION AND THE
FLORIDA PENINSULA EXTENDING ALSO OVER THE WESTERN ATLC...THE
BAHAMAS AND CUBA INTO THE NW CARIBBEAN. MOIST SLY WIND FLOW
BETWEEN THESE TWO UPPER-LEVEL FEATURES ALONG WITH A SURFACE
TROUGH EXTENDING ALONG 93W ARE GENERATING SCATTERED SHOWERS AND
ISOLATED TSTMS OVER THE WRN GULF W OF 93W AND THE WESTERN BAY OF
CAMPECHE. A COLD FRONT HAS ENTERED THE FAR NW GULF AND EXTENDS
FROM A WEAK 1020 MB LOW OVER NW LOUISIANA THROUGH THE DEEP SOUTH
TEXAS INTO THE NE PORTION OF MEXICO. MOSAIC DOPPLER RADAR FROM
THE SE U.S. DEPICTS A NARROW BAND OF SHOWERS WITH EMBEDDED TSTMS
ASSOCIATED WITH THE FRONT WHICH IS FORECAST TO MOVE SE ACROSS
THE REGION DURING THE NEXT FEW DAYS INCREASING WINDS AND SEAS.
THE FRONT WILL MOVE ACROSS SOUTH FLORIDA LATE SAT NIGHT AND
EARLY SUN...AND WILL LIKELY BECOME DIFFUSE FROM THE STRAITS OF
FLORIDA TO BAY OF CAMPECHE LATE SUN. HIGH PRESSURE CENTERED OVER
THE SE CONUS DOMINATES MUCH OF THE GULF E OF 90W...INCLUDING THE
FLORIDA PENINSULA AND STRAITS OF FLORIDA. STRONG SUBSIDENCE/DRY
AIR IS ALSO NOTED IN THE UPPER-LEVELS E OF 90W IN THE GULF. HIGH
PRES WILL BUILD IN BEHIND THE COLD FRONT.

CARIBBEAN SEA...
HURRICANE OMAR IS MOVING AWAY FROM THE NORTHERN LEEWARD ISLANDS
BUT IT IS STILL PRODUCING LOCALLY HEAVY RAIN OVER PORTIONS OF THE
NORTHERN AND CENTRAL LESSER ANTILLES FROM ANTIGUA SOUTHWARD TO
MARTINIQUE WHERE ADDITIONAL RAINFALL AMOUNTS OF 1 TO 3 INCHES...
WITH MAXIMUM AMOUNTS UP TO 6 INCHES ARE EXPECTED. SEE SPECIAL
FEATURES FOR MORE DETAILS. THE REMNANT CIRCULATION OF FORMER
TROPICAL DEPRESSION SIXTEEN PERSIST OVER NORTHERN HONDURAS WITH
MOST OF THE SHOWER ACTIVITY AFFECTING SOUTHERN BELIZE AND PARTS
OF GUATEMALA AND HONDURAS. A 1008 MB LOW WAS ANALYZED NEAR
16N86W ON THE 12Z SURFACE MAP. ALTHOUGH REFORMATION OF A
TROPICAL CYCLONE WILL NOT OCCUR DUE TO LAND INTERACTION...THIS
SYSTEM COULD STILL PRODUCE BRIEF PERIODS OF STRONG GUSTY
WINDS... ESPECIALLY OVER THE GULF OF HONDURAS...ALONG WITH
LOCALLY HEAVY RAINFALL. THESE RAINS COULD CAUSE FLASH FLOODS
ACROSS PORTIONS OF NICARAGUA...HONDURAS...EL
SALVADOR...BELIZE...AND GUATEMALA DURING THE NEXT COUPLE OF DAYS
AS THE SYSTEM MOVES WESTWARD AT AROUND 5 KT. A SFC TROUGH
EXTENDS FROM HURRICANE OMAR ACROSS THE EASTERN CARIBBEAN TO JUST
NORTH OF THE ABC ISLANDS. ISOLATED TO SCATTERED SHOWERS ARE
RELATED TO THIS FEATURE EAST OF 72W. SCATTERED MODERATE
CONVECTION IS OVER THE SW CARIBBEAN SOUTH OF 13N BETWEEN
75W-83W. UPPER DIFFLUENCE IS HELPING TO INDUCE THIS ACTIVITY. AS
PREVIOUSLY MENTIONED...THE UPPER-LEVEL HIGH LOCATED JUST NORTH
OF THE YUCATAN PENINSULA EXTENDS A RIDGE OVER THE WRN CARIBBEAN
SEA AND CENTRAL AMERICA S TO PANAMA AND CONTINUES TO ENHANCE
CONVECTION OVER THE AREA. WATER VAPOR IMAGERY REVEALS A DEEP
LAYERED TROUGH ACROSS THE W ATLC DIGGING SWD INTO THE CENTRAL
CARIBBEAN THROUGH HISPANIOLA. THIS TROUGH IS PRODUCING STRONG
VERTICAL SHEAR OVER OMAR AND  WILL LIKELY CONTINUE TO CAUSE A
DECREASE IN ITS INTENSITY. PATCHES OF LOW LEVEL CLOUDS WITH
POSSIBLE SHOWERS ARE REACHING PART OF CUBA AS WELL AS HISPANIOLA
AND PUERTO RICO UNDER A NLY WIND FLOW.

ATLANTIC OCEAN...
THE UPPER-LEVEL RIDGE CENTERED OVER THE GULF OF MEXICO ENVELOPS
THE W ATLC WATERS AND THE BAHAMAS W OF 70W. STRONG SUBSIDENCE IS
ASSOCIATED WITH THIS UPPER RIDGE BRINGING DRY AIR ACROSS THE
FLORIDA PENINSULA...THE BAHAMAS AND CUBA. A DEEP LAYERED TROUGH
EXTENDING FROM AN UPPER-LEVEL LOW LOCATED NEAR 33N59W ENTERS THE
CARIBBEAN SEA THROUGH HISPANIOLA. THE BASE OF THE TROUGH IS
REACHING 16N. THIS UPPER TROUGH SUPPORTS A SURFACE TROUGH THAT
EXTENDS FROM A 1008 MB LOW LOCATED NEAR 30N60W TO JUST NORTH OF
HURRICANE OMAR NEAR 23N61W. THIS LOW IS FORECAST TO DISSIPATE IN
ABOUT 24 HOURS. THE REMAINDER OF THE FORECAST AREA IS UNDER THE
INFLUENCE OF A SFC RIDGE ANCHORED ON A 1031 MB HIGH NEAR THE
AZORES. ALOFT...A RIDGE/TROUGH/RIDGE PATTERN IS SEEN OVER THE
CENTRAL AND EASTERN ATLC WITH RIDGES CENTERED NEAR 18N52W AND
INLAND OVER WEST AFRICA. BOTH RIDGES ARE SUPPORTING CONVECTION
ALONG THE ITCZ AXIS.

$$
GR






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