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Tropical Weather Discussion 9/17

By: Lindsey Day
By: Lindsey Day

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1115 UTC.

...SPECIAL FEATURES...
A 1009 MB LOW IS SSE OF THE CAPE VERDE ISLANDS NEAR 11N21W. THE LOW IS EMBEDDED WITHIN THE MONSOON TROUGH. AN AREA OF SCATTERED MODERATE/STRONG CONVECTION IS NEAR THE LOW CENTER FROM 10N-13N
BETWEEN 18W-26W. 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 18N16W TO A 1009 MB LOW NEAR 11N21W TO A SECOND 1012 MB LOW NEAR 10N38W AND ENDING NEAR 8N44W WHERE THE ITCZ CONTINUES TO 7N57W. SCATTERED MODERATE/STRONG CONVECTION IS IN THE VICINITY OF THE EASTWARD MOST LOW FROM 10N-13N BETWEEN 18W-26W.
ISOLATED MODERATE/STRONG CONVECTION IS S OF THE AXIS FROM 5N-10N BETWEEN 26W-33W...BECOMING MORE SCATTERED FROM 4N-9N BETWEEN 34W-43W. SCATTERED MODERATE/STRONG CONVECTION IS ALSO N OF THE AXIS FROM 14N-16N BETWEEN 32W-39W.

...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 30N94W. A FEW ISOLATED SHOWERS ARE ALONG THE BOUNDARY...AND TO THE S OF IT. 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 MOSTLY 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 FROM S OF WRN CUBA NEAR 21N83W TO ERN HONDURAS/NICARAGUA NEAR 13N84W. AN UPPER LEVEL TROUGH EXTENDING FROM HONDURAS AND ACROSS WRN CUBA IS PROVIDING AN AREA OF DIFFLUENCE OVER THE NW CARIBBEAN WHICH IS HELPING ENHANCE SHOWERS/THUNDERSTORMS JUST E OF THE YUCATAN
FROM 15N-20N BETWEEN 86W-89W...AND E OF THE SURFACE TROUGH FROM 11N-19N BETWEEN 77W-84W. SCATTERED SHOWERS/THUNDERSTORMS ARE ALSO S OF 13N BETWEEN 76W-81W ASSOCIATED WITH THE MONSOON TROUGH
WHICH EXTENDS ACROSS COSTA RICA TO NRN COLOMBIA. 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 CARIBBEAN UNDER MOSTLY FAIR CONDITIONS. HOWEVER...SCATTERED SHOWERS/THUNDERSTORMS ARE POPPING UP NEAR THE LOW CENTER N OF 15N BETWEEN 62W-70W AND AROUND THE ERN SIDE...SOME OF WHICH ARE APPROACHING THE WINDWARD
ISLANDS. 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 A SURFACE TROUGH E OF THE ISLANDS 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 JUST E OF NRN FLORIDA FROM 29N-31N BETWEEN 78W-81W. A SECOND AREA OF VERY
MOIST AIR IS ALONG A SURFACE TROUGH TO THE E ALONG 31N65W 27N72W ACROSS THE CENTRAL BAHAMAS TO 21N77W. STRONG SHOWERS/THUNDERSTORMS ARE NEAR THE SRN HALF OF THE TROUGH AXIS ACROSS THE BAHAMAS FROM 21N-27N BETWEEN 72W-78W...WITH ISOLATED
SHOWERS/THUNDERSTORMS WITHIN 90 NM EITHER SIDE OF THE TROUGH AXIS ELSEWHERE. AN UPPER LEVEL LOW SPINNING OVER THE VIRGIN ISLANDS IS SUPPORTING CLUSTERS OF SHOWERS/THUNDERSTORMS S OF 24N
BETWEEN 58W-69W. SCATTERED SHOWERS/THUNDERSTORMS ARE ALSO NEAR A SURFACE TROUGH E OF THE WINDWARD ISLAND ALONG 17N59W TO 11N60W WHICH LIES UNDER THE DIFFLUENT SIDE OF THE UPPER TROUGH/LOW.
FARTHER E...BROAD SURFACE RIDGING IS COVERING MOST OF THE ERN ATLC ANCHORED BY A 1021 MB HIGH NEAR 33N55W SUPPORTED BY AN UPPER LEVEL RIDGE CENTERED NEAR 36N51W...AND A 1029 MB HIGH N OF THE AZORES ISLANDS. HOWEVER...AN UPPER LEVEL LOW S OF THE AZORES
ISLANDS NEAR 34N33W IS SUPPORTING A SURFACE LOW PRESSURE SYSTEM N OF THE DISCUSSION AREA WHICH HAS A COLD FRONT EXTENDING ALONG 32N33W TO 30N41W. SCATTERED SHOWERS/THUNDERSTORMS ARE WITHIN 150
NM SE OF THE FRONTAL BOUNDARY. EXPECT THE SURFACE TROUGH IN THE WRN ATLC TO SLOWLY DRIFT WEST DURING THE NEXT 24 HOURS-06.


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