[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 170611
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT SAT SEP 17 2011

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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0515 UTC.

...SPECIAL FEATURES...
A 1012 MB LOW IS SSE OF THE CAPE VERDE ISLANDS NEAR 10N21W. THE
LOW IS EMBEDDED WITHIN THE MONSOON TROUGH AND HAS BECOME
SLIGHTLY BETTER ORGANIZED OVER THE PAST SEVERAL HOURS WITH AN
AREA OF SCATTERED MODERATE/STRONG CONVECTION NEAR THE LOW CENTER
FROM 10N-14N BETWEEN 20W-25W. SOME SLOW DEVELOPMENT IS POSSIBLE
OVER THE NEXT COUPLE OF DAYS AS THE LOW MOVES WWD AT 10-15 KT.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST OF SENEGAL
NEAR 14N17W TO A 1012 MB LOW NEAR 10N21W TO A SECOND 1012 M LOW
NEAR 9N37W AND ENDING NEAR 8N45W WHERE THE ITCZ BEGINS TO 8N56W.
SCATTERED MODERATE/STRONG CONVECTION IS IN THE VICINITY OF THE
EASTWARD MOST LOW FROM 10N-14N BETWEEN 20W-25W. ISOLATED
MODERATE/STRONG CONVECTION IS S OF THE AXIS FROM 5N-9N BETWEEN
25W-34W...BECOMING MORE SCATTERED FROM 6N-10N BETWEEN 34W-42W.

...DISCUSSION...

GULF OF MEXICO...
A DISSIPATING STATIONARY FRONT REMAINS ACROSS THE NRN GULF OF
MEXICO FROM THE BIG BEND OF FLORIDA NEAR 29N83W TO THE TEXAS
COAST NEAR 29N96W. A FEW ISOLATED SHOWERS ARE ALONG THE BOUNDARY
WITH ONE LARGER CLUSTER OVER NE FLORIDA POSSIBLY FURTHER
INFLUENCED BY DIFFLUENCE AROUND THE BASE OF A SHORTWAVE UPPER
TROUGH MOVING OFF THE ERN UNITED STATES COAST. UPPER LEVEL
RIDGING ACCOMPANIED BY MOSTLY DRY AIR COVERS THE GULF EXTENDING
FROM CENTRAL MEXICO TO NRN FLORIDA. THIS DRY AND STABLE AIR MASS
IS SUPPORTING FAIR WEATHER BASIN-WIDE WITH LIGHT ANTI-CYCLONIC
FLOW. THE FRONTAL BOUNDARY IS EXPECTED TO CONTINUE TO WEAKEN
THROUGHOUT THE NEXT 24 HOURS WITH WEAK ANTI-CYCLONIC SURFACE
FLOW REMAINING.

CARIBBEAN SEA...
A CONTRAST FROM THE GULF OF MEXICO...THE WRN CARIBBEAN IS LADEN
WITH DEEP LAYER MOISTURE. A SURFACE TROUGH IS ANALYZED JUST E OF
CENTRAL AMERICA ALONG 17N83W TO 11N81W. AN UPPER LEVEL TROUGH
EXTENDING FROM HONDURAS ACROSS WRN CUBA IS PROVIDING AN AREA OF
DIFFLUENCE OVER THE NW CARIBBEAN WHICH IS HELPING ENHANCE
SHOWER/THUNDERSTORM ACTIVITY IN THIS AREA. SCATTERED
SHOWERS/THUNDERSTORMS ARE FROM 17N-23N BETWEEN 75W-88W.
SCATTERED SHOWERS/ISOLATED THUNDERSTORMS ARE WITHIN 120 NM
EITHER SIDE OF THE SURFACE TROUGH AXIS. A STRONG CLUSTER OF
STORMS PREVIOUSLY OVER CENTRAL AMERICA HAS NOW BEGUN TO PUSH W
INTO THE E PACIFIC. ISOLATED SHOWERS ARE ALSO ALONG THE MONSOON
TROUGH WHICH EXTENDS ACROSS COSTA RICA TO NRN COLOMBIA. A
CLUSTER OF STRONGER SHOWERS/THUNDERSTORMS IS N OF THE AXIS FROM
11N-13N BETWEEN 75W-77W. AN UPPER LEVEL LOW IS DOMINATING THE
ERN CARIBBEAN CENTERED OVER THE VIRGIN ISLANDS. DRY AIR IS BEING
WRAPPED AROUND THE WRN SIDE OF THE UPPER LOW KEEPING THE CENTRAL
AND ERN CARIBBEAN UNDER MOSTLY FAIR CONDITIONS.
HOWEVER...SCATTERED SHOWERS/THUNDERSTORMS ARE POPPING UP NEAR
THE LOW CENTER AND AROUND THE ERN SIDE...SOME OF WHICH ARE
PUSHING S OVER PUERTO RICO AND ACROSS THE WINDWARD ISLANDS WHERE
A SURFACE TROUGH IS ANALYZED FROM 16N60W TO 11N62W. EXPECT MOIST
CONDITIONS TO REMAIN OVER THE WRN CARIBBEAN AND CENTRAL AMERICA.
THE UPPER LEVEL LOW OVER THE ERN CARIBBEAN IS EXPECTED TO REMAIN
SOMEWHAT STATIONARY...WITH THE SURFACE TROUGH EXPECTED TO MOVE
WWD WHICH WILL KEEP A CHANCE FOR SHOWERS/THUNDERSTORMS OVER THE
WINDWARD ISLANDS AND NRN LEEWARD ISLANDS.

ATLANTIC OCEAN...
AN UPPER LEVEL TROUGH OVER THE FAR WRN ATLC IS SUPPORTING A
STATIONARY FRONT WHICH JUST CLIPS THE AREA AND CROSSES ACROSS
NRN FLORIDA INTO THE GULF OF MEXICO. A CLUSTER OF
SHOWERS/THUNDERSTORMS IS ASSOCIATED WITH THE BOUNDARY ACROSS NE
FLORIDA AND THE IMMEDIATE COASTAL WATERS. AN AREA OF DRY AIR IS
SANDWICHED BETWEEN THIS FRONTAL BOUNDARY AND A SURFACE TROUGH TO
THE E ALONG 32N65W 27N71W ACROSS THE SE BAHAMAS TO 20N73W.
CLUSTERS OF SHOWERS/THUNDERSTORMS ARE WITHIN 120 NM OF THE
TROUGH WITH MORE CONCENTRATED ACTIVITY FROM 24N-27N BETWEEN
70W-76W...AND BETWEEN CUBA AND THE BAHAMAS FROM 21N-24N BETWEEN
74W-80W. AN UPPER LEVEL LOW SPINNING OVER THE VIRGIN ISLANDS IS
SUPPORTING CLUSTERS OF SHOWERS/THUNDERSTORMS N OF THE ISLANDS
FROM 18N-24N BETWEEN 61W-68W. ISOLATED SHOWERS ARE ALSO E OF THE
WINDWARD ISLANDS TO 54W IN THE DIFFLUENT AREA AROUND THE E SIDE
OF THE UPPER LOW/TROUGH. FARTHER E...BROAD SURFACE RIDGING IS
COVERING MOST OF THE ERN ATLC ANCHORED BY A 1024 MB HIGH NEAR
34N51W SUPPORTED BY AN UPPER LEVEL RIDGE CENTERED NEAR
36N51W...AND A 1031 MB HIGH N OF THE AZORES ISLANDS.
HOWEVER...AN UPPER LEVEL LOW S OF THE AZORES ISLANDS NEAR 34N32W
IS SUPPORTING A SURFACE LOW PRESSURE SYSTEM N OF THE DISCUSSION
AREA WHICH HAS A COLD FRONT EXTENDING ALONG 32N32W TO 29N36W.
SCATTERED SHOWERS/THUNDERSTORMS ARE WITHIN 120 NM SE OF THE
FRONTAL BOUNDARY. EXPECT THE SURFACE TROUGH IN THE WRN ATLC TO
SLOWLY DRIFT WEST DURING THE NEXT 24 HOURS.

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

$$
WALTON





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