[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 172354
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT THU SEP 17 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...SPECIAL FEATURES...
TROPICAL DEPRESSION NINE IS CENTERED NEAR 16.5N 44.8W AT 17/2100
UTC OR ABOUT 955 NM E OF THE LESSER ANTILLES MOVING N AT 6 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 1006 MB. MAXIMUM SUSTAINED
WIND SPEED IS 25 KT WITH GUSTS TO 35 KT. ISOLATED MODERATE
CONVECTION IS FROM 16N-20N BETWEEN 39W-45W. SEE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC
FOR MORE DETAILS.

A 1008 MB LOW IS W-SW OF THE CAPE VERDE ISLANDS CENTERED NEAR
12N34W MOVING W-NW AT 10-15 KT. ENVIRONMENTAL CONDITIONS ARE
EXPECTED TO BE CONDUCIVE FOR A TROPICAL DEPRESSION TO DEVELOP
DURING THE NEXT DAY OR TWO WITH A HIGH CHANCE OF TROPICAL
CYCLONE FORMATION OVER THE NEXT 48 HOURS. ISOLATED MODERATE
CONVECTION COVERS A BROAD AREA SURROUNDING THE LOW FROM 06N-16N
BETWEEN 25W-39W.

...TROPICAL WAVES...
TROPICAL WAVE EXTENDS FROM 10N82W TO 17N82W MOVING W AT 20 KT.
THE WAVE COINCIDES WITH 700 MB TROUGHING OVER THE SW CARIBBEAN
SEA AND CENTRAL AMERICA BETWEEN 79W-86W. SCATTERED MODERATE
CONVECTION IS FROM 05N-16N BETWEEN 77W-85W.

...ITCZ/MONSOON TROUGH...
THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST NEAR 13N17W TO
13N23W. THE INTERTROPICAL CONVERGENCE ZONE AXIS EXTENDS FROM
10N51W TO 09N61W. ASIDE FROM CONVECTION OCCURRING IN THE
VICINITY OF THE SPECIAL FEATURES MENTIONED ABOVE...ISOLATED
MODERATE CONVECTION IS FROM 10N-15N BETWEEN 20W-27W IN
ASSOCIATION WITH A WEAK SURFACE TROUGH ANALYZED FROM 11N21W TO
15N24W.

...DISCUSSION...

GULF OF MEXICO...
WATER VAPOR IMAGERY SHOWS A STARK CONTRAST IN ATMOSPHERIC
MOISTURE THIS EVENING DUE TO AN UPPER LEVEL TROUGH WITH AXIS
EXTENDING FROM OVER THE WESTERN CAROLINAS NEAR 25N82W S-SW TO A
BASE OVER THE EASTERN BAY OF CAMPECHE NEAR 19N91W. EAST OF THIS
TROUGH AXIS...A 1011 MB LOW IS CENTERED NEAR 26N84W WITH A
SURFACE TROUGH EXTENDING N TO 28N84W AND SW TO 23N88W. ANOTHER
SURFACE TROUGH IS ANALYZED IN THE OFFSHORE SW NORTH ATLC WATERS
OFF THE FLORIDA PENINSULA TO NEAR LAKE OKEECHOBEE TO NEAR
25N82W. BOTH BOUNDARIES AND THE LOW ARE PROVIDING FOCUS FOR
NUMEROUS SHOWERS AND SCATTERED TSTMS EAST OF A LINE FROM THE
FLORIDA BIG BEND REGION NEAR 30N84W TO THE NORTH-CENTRAL TIP OF
THE YUCATAN PENINSULA NEAR 22N88W. OTHERWISE...EAST OF THE UPPER
LEVEL TROUGH AXIS AND WEST OF THE PRIMARY WEATHER-PRODUCING
SURFACE FEATURES...MOSTLY CLEAR SKIES PREVAIL. WATER VAPOR
IMAGERY INDICATES VERY DRY AND SUBSIDENT CONDITIONS ALOFT DUE TO
NORTHERLY FLOW ON THE EASTERN PERIPHERY OF AN UPPER LEVEL RIDGE
ANCHORED OVER NORTHERN MEXICO NEAR 28N103W. THE OVERALL STABLE
CONDITIONS ALOFT CONTINUE TO SUPPORT A SURFACE RIDGE AXIS
EXTENDING FROM THE MISSISSIPPI RIVER VALLEY SW TO EAST-CENTRAL
MEXICO. THE LOW IN THE EASTERN GULF WILL GRADUALLY DRIFT
NORTHEASTWARD THROUGH LATE SATURDAY AND INTO THE SW NORTH ATLC
REGION BY EARLY SUNDAY.

CARIBBEAN SEA...
AN UPPER LEVEL RIDGE IS CENTERED OVER THE WESTERN CARIBBEAN NEAR
17N83W PROVIDING MOSTLY DRY CONDITIONS ALOFT WITH THE EXCEPTION
OF THE COASTAL NICARAGUA AND VICINITY. PRIMARILY THE RESULT OF A
TROPICAL WAVE ALONG 82W...INCREASED CLOUDINESS...SCATTERED
SHOWERS AND TSTMS ARE OCCURRING S OF 17N BETWEEN 79W-85W. IN
ADDITION...THE MONSOON TROUGH AXIS EXTENDING ALONG 10N/11N
BETWEEN NORTHERN COLOMBIA AND SOUTHERN COSTA RICA PROVIDING
ADDITIONAL LOW-LEVEL MOISTURE CONVERGENCE DYNAMICS. NORTH OF
THIS RIDGING...LATE AFTERNOON AND EARLY EVENING SCATTERED
SHOWERS AND TSTMS ARE OCCURRING ACROSS CUBA AND JAMAICA. THIS
ACTIVITY IS LIKELY DUE TO PEAK DAYTIME HEATING AND INSTABILITY
AND IS EXPECTED TO DIMINISH GRADUALLY THROUGH THE OVERNIGHT
HOURS. TO THE EAST OF THE RIDGE...AN UPPER LEVEL LOW IS CENTERED
NEAR 18N72W. MOST MOISTURE ASSOCIATED WITH THE LOW IS NOTED IN
THE FORM OF SCATTERED SHOWERS AND ISOLATED TSTMS ACROSS
HISPANIOLA AND PUERTO RICO...INCLUDING THE ADJACENT COASTAL
WATERS N OF 16N BETWEEN 64W-73W. OTHERWISE...MODERATE TO FRESH
TRADES PREVAIL WITH OCCASIONAL STRONG BREEZE CONDITIONS
OCCURRING WITHIN CLOSE PROXIMITY TO THE COAST OF NE COLOMBIA AND
NW VENEZUELA.

...HISPANIOLA...
AN UPPER LEVEL LOW IS CENTERED OVER EASTERN HISPANIOLA NEAR
18N72W PROVIDING INCREASED MOISTURE...CLOUDINESS...AND SCATTERED
SHOWERS AND ISOLATED TSTMS ACROSS THE ISLAND AND ADJACENT
COASTAL WATERS. WITH THE UPPER LEVEL FEATURE FORECAST TO SLOWLY
MOVE SOUTHWARD THROUGH SUNDAY...INCREASED PROBABILITY OF
SCATTERED AFTERNOON AND EVENING SHOWERS AND TSTMS ARE EXPECTED
THROUGH THE UPCOMING WEEKEND.

ATLANTIC OCEAN...
WITH AN UPPER LEVEL TROUGH AXIS EXTENDING FROM OVER THE WESTERN
CAROLINAS S-SW TO THE SW GULF OF MEXICO...MIDDLE TO UPPER LEVEL
DIFFLUENCE IS MAXIMIZED OVER MUCH OF THE SW NORTH ATLC THIS
EVENING DUE TO SOUTHWESTERLY FLOW BETWEEN THE TROUGHING AND AN
UPPER LEVEL RIDGE ANCHORED NEAR 27N73W. NUMEROUS SHOWERS AND
SCATTERED TSTMS ARE OCCURRING N OF 25N W OF 70W. FARTHER EAST...
AN UPPER LEVEL TROUGH IS NOTED OVER THE CENTRAL NORTH ATLC WITH
SHORTWAVE ENERGY LOCATED IN THE VICINITY OF 28N57W. THE
TROUGHING SUPPORTS A COLD FRONT EXTENDING FROM 24N44W TO 30N52W
AND A SURFACE TROUGH EXTENDING FROM THE COLD FRONT NEAR 31N50W
TO 27N51W. ISOLATED SHOWERS ARE OCCURRING WITHIN 60 NM EITHER
SIDE OF THE COLD FRONT AND SURFACE TROUGH BOUNDARIES. FINALLY...
A WEAKENING COLD FRONT IS ANALYZED OVER THE NE ATLC PORTION OF
THE DISCUSSION AREA FROM 31N10W TO 30N20W TO 32N27W. ISOLATED
SHOWERS ARE POSSIBLE WITHIN 90 NM EITHER SIDE OF THE FRONT.
OTHERWISE...THE EASTERN ATLC IS UNDER THE INFLUENCE OF A 1019 MB
HIGH CENTERED NEAR 28N30W.

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

$$
HUFFMAN
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