[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 171749
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT FRI OCT 17 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...
OMAR WAS DOWNGRADED TO A TROPICAL STORM AT 17/0300 UTC. TWELVE
HOURS LATER...AT 17/1500 UTC THE CENTER OF TROPICAL STORM OMAR
IS NEAR 28.9N 55.1W OR ABOUT 545 NM...1000 KM...EAST-SOUTHEAST
OF BERMUDA MOVING NE OR 035 DEG AT 30 KT. THE SYSTEM IS EXPECTED
TO CONTINUE MOVING IN THIS GENERAL DIRECTION WITH A DECREASE IN
FORWARD SPEED DURING THE NEXT 48 HOURS. ESTIMATED MINIMUM
CENTRAL PRESSURE IS 987 MB. MAXIMUM SUSTAINED WIND SPEED IS 60
KT WITH GUSTS TO 75 KT. SOME SMALL FLUCTUATIONS IN INTENSITY ARE
POSSIBLE IN THE NEXT 24 HOURS WITH GRADUAL WEAKENING OCCURRING
ON SATURDAY. 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. THE CYCLONE HAS DEVELOPED A STRONG CURVED BAND
THIS MORNING...AND HAS A SHORT WINDOW OF OPPORTUNITY TO BECOME A
MINIMAL HURRICANE TODAY BEFORE REACHING COOLER WATERS AND UNDER
MUCH STRONGER SHEAR IN ABOUT 24 HOURS. LATEST SATELLITE IMAGERY
INDICATES THAT CONVECTION IS ALREADY DIMINISHING NEAR THE OMAR'S
CENTER.

...TROPICAL WAVES...
A TROPICAL WAVE IS ALONG 30W/31W S OF 16N MOVING W 10-15 KT.
THIS WAVE SHOWS UP VERY WELL ON THE TPW PRODUCT FROM CIMSS WHERE
A NORTH-SOUTH MOISTURE MAXIMUM IS SEEN. WELL-DEFINED CYCLONIC
CURVATURE IS EVIDENT ON SATELLITE IMAGERY WITH A VERY LARGE AREA
OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION FROM 5N-15N
BETWEEN 22W-35W. FURTHER DEVELOPMENT OF THIS SYSTEM IS NOT
EXPECTED DURING THE NEXT 48 HOURS OR SO DUE TO THE PRESENCE OF
AN UPPER-LEVEL LOW AHEAD OF THE WAVE AXIS.

A TROPICAL WAVE IS ALONG 51W/52W S OF 15N MOVING W 10-15 KT. THE
WAVE IS OBSERVED ON THE SSMI-TPW PRODUCT FROM CIMSS AND REMAINS
EMBEDDED WITHIN THE ITCZ. SCATTERED MODERATE CONVECTION IS FROM
7N-11N BETWEEN 50W-55W. THERE ARE NO SIGNS OF ORGANIZATION AND
DEVELOPMENT...IF ANY...WILL BE SLOW TO OCCUR.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 8N13W 9N27W 7N40W 9N50W 8N60W. IN
ADDITION TO CONVECTION ASSOCIATED WITH THE TROPICAL WAVES...A
CLUSTER OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS NEAR
9N16W. SIMILAR CONVECTION IS 12N40W AND FROM 7N-10N BETWEEN
56W-58W.

...DISCUSSION...

GULF OF MEXICO...
A COLD FRONT EXTENDS ACROSS SE LOUISIANA TO 28N94W...THEN
CONTINUES AS A STATIONARY FRONT ACROSS THE WESTERN GULF ENTERING
MEXICO JUST SOUTH OF TAMPICO. A BAND OF MULTILAYERED CLOUDS WITH
EMBEDDED SHOWERS IS ASSOCIATED WITH THE FRONT OVER THE NW CORNER
OF THE GULF WHILE A BAND OF MAINLY LOW CLOUDS DEFINES THE FRONT
OVER MEXICO. A SHORT-WAVE TROUGH EXTENDING OVER THE DEEP SOUTH
TEXAS AND NE MEXICO SUPPORTS THIS FRONTAL SYSTEM WHILE A DEEP
LAYERED TROUGH IS OVER THE CENTRAL CONUS. MOIST SWLY FLOW IS
OVER THE NW QUADRANT OF THE GULF AHEAD OF THIS TROUGH. AN UPPER
LEVEL RIDGE ANCHORED IN THE CENTRAL GULF NEAR 24N89W COVERS THE
E-CENTRAL GULF AND THE FLORIDA PENINSULA PRODUCING A DRY AND
STABLE ATMOSPHERE DUE TO THE SUBSIDENCE. AT THE SURFACE...A WEAK
1021 MB HIGH PRESSURE CENTERED OVER THE NE GULF AND NORTHERN
FLORIDA CONTROLS THE EASTERN HALF OF THE GULF...INCLUDING THE
FLORIDA PENINSULA AND STRAITS OF FLORIDA. AS A RESULT...WINDS
HAVE DIMINISHED ACROSS THE AREA COMPARED WITH THE PREVIOUS DAYS.

CARIBBEAN SEA...
A BROAD AND ELONGATED AREA OF LOW PRES COVERS THE CENTRAL AND
WESTERN CARIBBEAN WITH TWO CENTERS. ONE IS A 1011 MB LOW LOCATED
NEAR 16N75W AND THE SECOND ONE IS SPINNING OVER THE GULF OF
HONDURAS. A SFC TROUGH THAT EXTENDS WWD FROM THE NORTHERN
LEEWARD ISLANDS ACROSS THE CARIBBEAN ALONG ROUGHLY 16N CONNECTS
THE ABOVE MENTIONED LOW CENTERS. ISOLATED TO SCATTERED MODERATE
CONVECTION IS ASSOCIATED WITH THE TROUGH OVER THE NE CARIBBEAN
AND WITH THE LOW CENTERS. THE FIRST LOW IS FORECAST TO
DISSIPATE BY SAT...WHILE THE LOW OVER THE GULF OF HONDURAS WILL
REMAIN NEARLY STATIONARY DURING THE UPCOMING WEEKEND THEN WILL
SLOWLY MOVE NWD THROUGH WED. ON THE OTHER HAND...THE REMNANT
CIRCULATION OF FORMER TROPICAL DEPRESSION SIXTEEN IS CENTERED
INLAND NEAR EL SALVADOR/GUATEMALA BORDER. THIS SYSTEM CONTINUES
TO PRODUCE LOCALLY HEAVY RAINS FROM NICARAGUA TO SOUTHEASTERN
MEXICO. THESE RAINS COULD CAUSE FLASH FLOODS AND MUD SLIDES.
THIS LOW IS EXPECTED TO MOVE INTO THE EPAC PRETTY SOON.
STRONG SUBSIDENCE/DRY AIR IS ACROSS HISPANIOLA...JAMAICA...CUBA
AND THE NRN YUCATAN PENINSULA THANKS TO THE UPPER-LEVEL RIDGE
CENTERED OVER THE CENTRAL GULF OF MEXICO NEAR 24N89W. AN
UPPER-LEVEL LOW REMAINS N OF THE EASTERN TIP OF DOMINICAN
REPUBLIC WHILE AN UPPER LEVEL RIDGE AXIS EXTENDS FROM THE
CENTRAL ATLC ACROSS THE WINDWARD ISLANDS TO NE VENEZUELA AND IS
PROVIDING UPPER DIFFLUENCE TO AID IN SUPPORTING THE
PRECIPITATION ALONG THE AFOREMENTIONED SURFACE TROUGH.

ATLANTIC OCEAN...
THE UPPER-LEVEL RIDGE ACROSS THE GULF OF MEXICO AND THE FLORIDA
STATE EXTENDS INTO THE W ATLC AND THE BAHAMAS. STRONG SUBSIDENCE
IS ASSOCIATED WITH THIS UPPER RIDGE BRINGING DRY AIR ALSO ACROSS
THE BAHAMAS AND CUBA. HIGH PRES ALSO DOMINATES THE AREA AT THE
SURFACE. FURTHER EAST IS T.S. OMAR MOVING RAPIDLY TO THE NE. THE
REMAINDER OF THE ATLANTIC FORECAST AREA IS UNDER THE INFLUENCE
OF A SFC RIDGE ANCHORED ON A 1028 MB HIGH NEAR 35N31W. ALOFT...A
RIDGE/TROUGH/RIDGE PATTERN IS OBSERVED OVER THE CENTRAL AND E
ATLC WITH RIDGES CENTERED NEAR 28N45W AND INLAND OVER W AFRICA.
IN BETWEEN...THERE IS AN UPPER-LEVEL LOW NEAR 17N38W. BOTH
RIDGES ARE SUPPORTING CONVECTION ALONG THE ITCZ AXIS.

$$
GR






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