[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 181744
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU OCT 18 2012

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...WEATHER OBSERVATIONS...RADAR...AND
METEOROLOGICAL ANALYSIS.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1615 UTC.

...TROPICAL WAVES...

WEAK TROPICAL WAVE IS ALONG 15N45W TO 8N45W MOVING WEST NEAR 15
KT. DUE TO A LARGE UPPER TROUGH JUST WEST OF THE WAVE...IT IS
HARD TO DISCERN WHETHER CONVECTION NEAR THE AXIS IS ASSOCIATED
WITH THE WAVE OR THE UPPER TROUGH. IT IS MOST LIKELY TIED TO THE
UPPER TROUGH DUE TO THE FACT THAT THE WAVE HAS BEEN WEAK. EITHER
WAY...SCATTERED MODERATE CONVECTION IS FROM 8N-11N BETWEEN
45W-47W...AND FROM 11N-15N BETWEEN 47W-52W.

...THE ITCZ/THE MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS ACROSS WEST AFRICA TO THE COAST OF
SENEGAL AT 13N17W CONTINUING ALONG 9N24W 8N29W. THE ITCZ BEGINS
AT 8N29W AND ENDS NEAR 10N39W. ISOLATED MODERATE CONVECTION IS
WITHIN 150 NM N OF THE AXIS BETWEEN 20W-30W.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER LEVEL TROUGH COVERING THE EASTERN CONUS SUPPORTS A COLD
FRONT THAT IS JUST BEGINNING TO MOVE INTO THE GULF OF MEXICO. AS
OF 1500 UTC...IT EXTENDS FROM THE FLORIDA/ALABAMA BORDER AT
31N88W ACROSS SE LOUISIANA TO 28N93W TO THE TEXAS COAST AT
27N97W. A LINE OF SHOWERS/POSSIBLE THUNDERSTORMS IS ALONG THE
AXIS AND EXTEND UP TO 100 NM AHEAD OF THE FRONT EAST OF 90W.
BESIDES MOISTURE IMMEDIATELY ALONG THE FRONT...THE REMAINDER OF
THE BASIN IS UNDER THE INFLUENCE OF MOSTLY DRY AIR ALOFT AROUND
AN UPPER LEVEL RIDGE CENTERED OVER CENTRAL MEXICO. THE DRY AIR
IS HELPING MAINTAIN CLEAR SKIES EXCEPT FOR A FEW
SHOWERS/THUNDERSTORMS IN THE SE GULF NEAR A WEAK SURFACE TROUGH
ALONG 27N83W TO 23N85W. THE FRONT IS EXPECTED TO CONTINUE MOVING
SE...AND SHOULD EXTEND FROM NE FLORIDA TO NE MEXICO IN 24
HOURS...AND SHOULD MOVE OUT OF THE BASIN BY THE END OF THE
WEEKEND. SURFACE RIDGING WILL BUILD IN BEHIND THE FRONT.

CARIBBEAN SEA...
MOSTLY DRY AIR ALOFT COVERS THE NW CARIBBEAN AROUND AN UPPER
LEVEL RIDGE EXTENDING FROM MEXICO ACROSS THE YUCATAN AND INTO
THE AREA PROVIDING FAIR CONDITIONS N OF 16N WEST OF 74W. THE
REMAINDER OF THE BASIN IS COVERED BY A SECOND BROAD AND
ELONGATED UPPER LEVEL RIDGE THAT EXTENDS FROM THE SW CARIBBEAN
TO THE NE CARIBBEAN. MODERATE MOISTURE ACCOMPANIES THE UPPER
RIDGE AND IS HELPING PRODUCE ISOLATED SHOWERS ACROSS MUCH OF THE
SW AND EASTERN CARIBBEAN. THE ACTIVITY IN THE SW CARIBBEAN IS
ALSO ENHANCED BY THE PRESENCE OF THE MONSOON TROUGH THAT EXTENDS
FROM SOUTHERN NICARAGUA TO NORTHERN COLOMBIA ALONG 11N. A WEAK
SURFACE TROUGH IS ALSO IN THE EASTERN CARIBBEAN ALONG 15N63W TO
11N63W HELPING PRODUCE MORE SCATTERED SHOWER ACTIVITY IN ITS
VICINITY. EXPECT LITTLE CHANGE OVER THE NEXT 24 HOURS.

ATLANTIC OCEAN...
AN UPPER LEVEL TROUGH IS MOVING INTO THE WEST ATLC WITH AXIS
ALONG 80W. A SHORTWAVE TROUGH EXTENDS OFF THE MAIN LONGWAVE
HELPING PRODUCE SHOWERS/THUNDERSTORMS FROM 25N-27N BETWEEN
75W-77W...AND FROM 25N-28N BETWEEN 71W-74W. A FEW ISOLATED
PATCHES OF SHOWERS/THUNDERSTORMS ARE ALSO OFF THE FLORIDA COAST
FROM 24N-29N. FARTHER EAST...AN UPPER LEVEL RIDGE EXTENDS FROM
THE NE CARIBBEAN INTO THE CENTRAL ATLC ALONG 58W DRAWING UP AN
AREA OF MOISTURE. AT THE SURFACE...A SURFACE TROUGH EXTENDS FROM
NEAR 31N56W TO 22N64W...WHICH IS AN EXTENSION OF A COLD FRONT IN
THE NORTHERN ATLC. SCATTERED SHOWERS ARE EAST OF THE SURFACE
TROUGH AXIS WITHIN 200 NM. THE REMAINDER OF THE BASIN IS COVERED
BY A BROAD SURFACE RIDGE ANCHORED BY A 1026 MB HIGH NEAR 36N36W.
THE SURFACE RIDGE IS SUPPORTED BY AN UPPER LEVEL RIDGE COVERING
THE EASTERN TROPICAL ATLC WITH AXIS ALONG 22N32W. A BROAD UPPER
LEVEL LOW IS CENTERED TO THE WEST NEAR 18N50W...WHICH IS
PROVIDING DIFFLUENCE ALOFT NEAR A TROPICAL WAVE TO THE SOUTH. IT
IS ALSO HELPING PRODUCE AN AREA OF SHOWERS/POSSIBLE
THUNDERSTORMS FROM 15N-18N BETWEEN 36W-38W. IN THE FAR NE CORNER
OF THE DISCUSSION AREA...A COLD FRONT EXTENDS FROM SPAIN INTO
THE AREA ALONG 32N11W TO 29N19W. SCATTERED SHOWERS ARE UP TO 100
NM AHEAD OF THE FRONT.

FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE

$$
WALTON





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