[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 201747
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT TUE OCT 20 2015

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
1715 UTC.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH AXIS EXTENDS FROM THE AFRICAN COAST NEAR
13N17W SW 09N21W...THEN W TO 09N29W TO A 1011 MB LOW NEAR 10N33W
TO ANOTHER 1011 MB LOW NEAR 10N40W AND TO 10N44W. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 150 NM SE OF THE
TROUGH BETWEEN 17W-18W...AND WITHIN 120 NM S OF THE TROUGH
BETWEEN 37W-39W. SCATTERED MODERATE CONVECTION IS WITHIN 30 NM
OF THE TROUGH BETWEEN 24W-27W...AND ALSO BETWEEN 33W-34W.

...DISCUSSION...

GULF OF MEXICO...
THE TAIL END OF THE ATLC WEAKENING STATIONARY FRONT EXTENDS FROM
S FLORIDA TO NEAR 25N85W. SCATTERED SHOWERS AND POSSIBLE
ISOLATED WEAK THUNDERSTORMS MOVING QUICKLY WESTWARD ARE S OF THE
FRONT. A SURFACE TROUGH IS OVER THE WESTERN GULF ALONG 92W/93W
FROM 20N-25N AS OF 15 UTC. THE PRESSURE GRADIENT BETWEEN HIGH
PRESSURE OVER THE EASTERN GULF AND BROAD LOW PRESSURE ASSOCIATED
WITH THIS TROUGH WILL MAINTAIN STRONG EASTERLY WINDS ACROSS THE
E CENTRAL GULF WATERS THROUGH TONIGHT. THIS GRADIENT IS FORECAST
TO WEAKEN ON WED. GENTLE TO MODERATE E-SE FLOW WILL PREVAIL OVER
THE NW GULF.

CARIBBEAN SEA...
UPPER-LEVEL RIDGING EXTENDS OVER CENTRAL AMERICA IS COVERING THE
WESTERN HALF OF THE BASIN WHILE AN ELONGATED UPPER-LEVEL TROUGH
EXTENDS NEWD ACROSS THE TROPICAL ATLANTIC. AT THE SURFACE...A
SURFACE TROUGH IS ANALYZED FROM JUST INLAND THE NE YUCATAN
PENINSULA TO ALONG THE COAST OF BELIZE AND TO INLAND THE NW PART
OF HONDURAS. SCATTERED MODERATE CONVECTION IS OBSERVED JUST W OF
THE TROUGH...AND FROM 14N-20N BETWEEN 82W AND THE TROUGH DUE TO
UPPER DIFFLUENT FLOW ALOFT AND LOW-LEVEL CONVERGING MOISTURE
WITHIN THE MODERATE TO FRESH TRADES OVER THAT PART OF THE SEA.
OTHER DIFFLUENT FLOW ALOFT IS ALSO NOTED OVER MUCH OF CUBA AND
HISPANIOLA SUPPORTING ISOLATED MODERATE CONVECTION ACROSS SOME
SECTIONS OF CUBA....AND OTHER CONVECTION AS DESCRIBED BELOW
UNDER HISPANIOLA SECTION. DRY AIR AND SUBSIDENCE PERSISTS ACROSS
THE CENTRAL AND EASTER CARIBBEAN INHIBITING CONVECTION EXCEPT
DIURNAL ACTIVITY OVER THE GREATER ANTILLES. GENERALLY MODERATE
TRADE WINDS COVER THE CENTRAL AND EASTERN CARIBBEAN. CONVECTION
WILL CONTINUE OVER THE NW CARIBBEAN OVER THE NEXT 24 TO AT LEAST
36 HOURS.

...HISPANIOLA...
A DIFFLUENT PATTERN ALOFT JUST N OF THE ISLAND ALONG THE BASE OF
AN ATLC MID/UPPER TROUGH CONTINUES TO PROVIDE UPPER VENTILATION
FOR SCATTERED MODERATE/ISOLATED STRONG CONVECTION THAT IS JUST N
AND INLAND THE N CENTRAL COAST OF THE ISLAND. ISOLATED SHOWERS
AND THUNDERSTORMS ARE DEVELOPING JUST OFFSHORE THE REST OF THE
ISLANDS. LATEST SURFACE OBSERVATIONS FROM MDPP ARE REPORTING
CUMULONIMBUS TYPE CLOUDS WITH POSSIBLE DEVELOPING TSTMS AT ALL
QUADRANTS. THESE CLOUDS AND ACTIVITY ARE EXPECTED TO FURTHER
INTENSIFY THROUGHOUT THE AFTERNOON AS DAYTIME HEATING GETS
UNDERWAY. CIRRUS OUTFLOW FROM THE SCATTERED MODERATE/ISOLATED
STRONG CONVECTION MAY INHIBIT CONVECTION FROM DEVELOPING SOME
OVER PORTIONS OF THE HAITI/DOMINICAN REPUBLIC BORDER. EXPECT AN
INCREASE IN CONVECTION THROUGH THE NEXT 48 HOURS AS THE ATLC
TROUGH AMPLIFIES...AND THE FAVORABLE DIFFLUENT PATTERN BECOMES
MORE PRONOUNCED WHILE AT THE SAME TIME GFS PRECIPITABLE
POTENTIAL GUIDANCE DEPICTS INCREASING MOISTURE VALUES FOR THE
ISLAND.

ATLANTIC OCEAN...
A BROAD MID/UPPER-LEVEL TROUGH SLIDING EASTWARD ACROSS THE NW
ATLANTIC CONTINUES TO SUPPORT TO A FRONTAL SYSTEM THAT BEGINS AS
A WEAKENING STATIONARY FRONT THAT EXTENDS FROM S FLORIDA TO
25N74W TO 25N62W WHERE IT THEN TRANSITIONS INTO A COLD FRONT
THAT CONTINUES NE TO 26N60W AND TO NE OF THE AREA AT 32N49W. A
PRE-FRONTAL TROUGH IS SE OF THE COLD FRONT ALONG A POSITION FROM
30N51W TO 25N60W...AND CONTINUES SW TO NEAR 21N69W. ASCAT DATA
FROM 1310 UTC THIS MORNING SHOWED A SHARP S TO NE WIND SHIFT
ACROSS THE TROUGH. UPPER LEVEL DYNAMIC LIFT PROVIDED BY THE
MID/UPPER TROUGH COMBINING WITH PLENTIFUL MOISTURE BETWEEN THE
FRONT AND PRE-FRONTAL TROUGH IS RESULTING IN CLUSTERS OF
SCATTERED MODERATE/ISOLATED STRONG CONVECTION FROM 21N-24N
BETWEEN 63W-69W...AND FROM 24N-28N BETWEEN 54W-63W. OTHER
SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS NEAR THE BASE
OF THE MID/UPPER TROUGH FROM 20N-23N BETWEEN 71W-74W...AND
BETWEEN THE CENTRAL BAHAMAS AND THE N CENTRAL COAST OF CUBA. THE
COLD FRONT PORTION OF FRONTAL BOUNDARY WILL CONTINUE SE TONIGHT
STALLING FROM 26N65W TO THE WINDWARD PASSAGE ON WED AND THU. A
WEAK LOW WILL DEVELOP ALONG THE FRONT NEAR 23N69W ON THU NIGHT
AND RACE NE DRAGGING THE FRONT E AGAIN ON FRI. THE FRONT WILL
BECOME STATIONARY OVER THE FAR SE WATERS N OF PUERTO RICA ON
SAT...THEN DRIFT W ON SUN.

A MORE STABLE UPPER LEVEL ENVIRONMENT W OF THE MID/UPPER TROUGH
IS ALLOWING FOR MAINLY SCATTERED TO NUMEROUS SHOWERS TO EXIST
ALONG AND NEAR THE STATIONARY FRONTAL BOUNDARY. THESE SHOWERS
ARE MOVING WESTWARD RATHER QUICKLY...AND ARE CAPABLE OF
PRODUCING GUSTY WINDS.

OVER THE TROPICAL ATLC PORTION...A SURFACE TROUGH IS ROUGHLY
ALONG A POSITION FROM NEAR 15N53W TO 12N55W TO 09N55W. THIS
FEATURE IS INTERACTING WITH AN UPPER-LEVEL TROUGH THAT EXTENDS
FROM THE WINDWARD ISLANDS NE TO NEAR 20N53W. A DIFFLUENT FLOW
ALOFT E OF THE UPPER TROUGH IS SUPPORTING ISOLATED CONVECTION E
OF THIS SURFACE TROUGH FROM 11N-18N BETWEEN 43W-53W. HOWEVER
...THIS CONVECTION IS SHORT-LIVED AS UPPER LEVEL SW WINDS ARE
SHEARING OFF THE CLOUDS TOPS OFF TO THE E. OVER THE FAR EASTERN
ATLC...A DISSIPATING COLD FRONT EXTENDS FROM

OVER THE FAR EASTERN ATLC...A COLD FRONT FROM OVER NW AFRICA
EXTENDS SW TO 23N17W AND TO 23N22W. ISOLATED SHOWERS ARE
POSSIBLE ALONG THE FRONT MAINLY BETWEEN 19W-22W. NEAR GALE FORCE
WINDS ARE POSSIBLE N OF 32N E OF 15W DUE TO A STRONG PRESSURE
GRADIENT BEHIND THIS COLD FRONT.

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

$$

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