[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 131801
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SAT JUL 13 2013

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.

...TROPICAL WAVES...
TROPICAL WAVE IS JUST EAST OF DAKAR SENEGAL AND EXTENDS FROM
18N16W TO 10N17W MOVING W AT 10 KT. THE HOVMOLLER DIAGRAM SHOWS
THE WESTWARD MOVEMENT OF THE WAVE THAT COINCIDES WITH A SURGE OF
MOISTENED AIR AS DEPICTED ON THE TOTAL PRECIPITABLE WATER
IMAGERY. SCATTERED MODERATE CONVECTION IS NOTED WHERE THE WAVE
AXIS MEETS THE MONSOON TROUGH FROM 9N-12N BETWEEN 17W-20W.

TROPICAL WAVE IN THE CENTRAL TROPICAL ATLC EXTENDS FROM 20N37W
TO 10N38 MOVING W AT 10 KT. THE WAVE REMAINS EMBEDDED WITHIN A
SURGE OF MOISTURE AS DEPICTED ON THE TOTAL PRECIPITABLE WATER
IMAGERY. NO DEEP CONVECTION IS NOTED. ONLY FEW SHOWERS ARE NEAR
THE SOUTHERN END OF THIS WAVE WHICH IS FORECAST TO MOVE ACROSS
THE TROPICAL N ATLC MON AND INTO THE EASTERN CARIBBEAN TUE.

TROPICAL WAVE IN THE W CARIBBEAN EXTENDS FROM CABO SAN ANTONIO
CUBA TO NORTHERN HONDURAS NEAR 15N86W. AN EARLIER ASCAT PASS
CLEARLY SHOWED THE WIND SHIFT ASSOCIATED WITH THE WAVE AXIS.
MOST OF THE CONVECTION RELATED TO THE WAVE IS DISPLACED TO THE
EAST DUE TO MODERATE TO STRONG WESTERLY WINDS ALOFT. A CLUSTER
OF MODERATE TO ISOLATED STRONG CONVECTION COVERS THE AREA FROM
16N TO 19N BETWEEN 81W AND 84W. THE WAVE IS EXPECTED TO REACH
THE YUCATAN PENINSULA TONIGHT.

...ITCZ/MONSOON TROUGH...                                     A
MONSOON TROUGH EXTENDS FROM 10N19W TO 8N23W TO 9N28W. THE ITCZ
CONTINUES FROM 9N28W TO 11N35W THEN RESUMES W OF THE TROPICAL
WAVE ALONG 37W/38W EXTENDING FROM 10N40W TO 8N50W TO NE GUYANA
NEAR 7N58W. ISOLATED TO SCATTERED MODERATE CONVECTION IS WITHIN
180 NM S OF THE MONSOON TROUGH BETWEEN 19W AND 28W. SIMILAR
CONVECTION IS WITHIN 180 NM S OF THE ITCZ AXIS FROM 49W TO 52W
AND WITHIN 150 NM N OF THE ITCZ AXIS BETWEEN 55W AND 57W.

...DISCUSSION...

GULF OF MEXICO...
WEAK PRES GRADIENT PREVAILS ACROSS THE GULF WATERS. A 1012 MB
LOW IS OVER THE NE GULF OF MEXICO NEAR 28.5N88W. A SURFACE
TROUGH EXTENDS FROM THE LOW CENTER TO NEAR 23N88W. A SECOND
TROUGH STRETCHES FROM THE SAME LOW PRES E THEN NE TO A WEAK 1014
MB LOW PRES OVER SE GEORGIA NEAR 31.5N81W. DOPPLER RADAR SHOWS
SCATTERED SHOWERS AND TSTMS AHEAD OF THE FIRST TROUGH AXIS
MAINLY N OF 26N AFFECTING THE NE GULF WATERS...INCLUDING THE
FLORIDA BIG BEND AND PARTS OF N FLORIDA. A WEAK 1015 MB HIGH
PRES IS ANALYZED NEAR 26N95W. THE LOW PRES WILL DRIFT NORTHWARD
AND WEAKEN TONIGHT. A WEAK RIDGE WILL DOMINATE THE GULF REGION
ON SUN. ALOFT...AN UPPER LEVEL TROUGH OVER THE SE CONUS ENTERS
THE GULF NEAR MOBILE ALABAMA AND EXTENDS TO NEAR 25N93W
SUPPORTING THE AFOREMENTIONED SURFACE LOW AND TROUGH. ANOTHER
TROUGH IS SEEN FARTHER SOUTH AND EXTENDS FROM NEAR 24N87W TO
22N92W TO 23N97W. MAINLY WESTERLY WINDS ARE ON THE SOUTHERN SIDE
OF THIS TROUGH OVER THE SW GULF...THE YUCATAN PENINSULA AND THE
NW CARIBBEAN.

CARIBBEAN SEA...
AS PREVIOUSLY MENTIONED...A TROPICAL WAVE IS OVER THE WESTERN
CARIBBEAN. SEE TROPICAL WAVES SECTION FOR DETAILS. A SURFACE
TROUGH WAS ANALYZED ON THE 12Z SURFACE MAP OVER THE EASTERN
CARIBBEAN AND RUNS FROM 20N62W TO 12N64W. THIS TROUGH...
REFLECTION OF A MID TO UPPER LEVEL TROUGH WILL MOVE ACROSS THE
UK/US VIRGIN ISLANDS AND PUERTO RICO THIS AFTERNOON AND TONIGHT.
PATCHES OF LOW LEVEL MOISTURE ARE ASSOCIATED WITH THIS TROUGH.
MODERATE TO FRESH TRADE WINDS ARE BLOWING ACROSS THE SOUTH-
CENTRAL CARIBBEAN PER THE MOST RECENT SURFACE DATA. WINDS ARE
EXPECTED TO SLIGHTLY INCREASE ON MON AS HIGH PRES BUILDS
WESTWARD N OF AREA. SHALLOW MOISTURE EMBEDDED IN THE TRADE WIND
FLOW WILL MOVE ACROSS THE E AND CENTRAL CARIBBEAN PRODUCING
ISOLATED TO SCATTERED PASSING SHOWERS. CONVECTION INCREASES OVER
THE WESTERN CARIBBEAN DUE TO THE PRESENCE OF THE TROPICAL WAVE.
ALOFT...A RIDGE/TROUGH/RIDGE PATTERN DOMINATES THE BASIN. A
RIDGE EXTENDS FROM NORTHERN CENTRAL AMERICA ALL THE WAY NE
THROUGH EASTERN CUBA INTO THE BAHAMAS. A TROUGH STRETCHES FROM
DOMINICAN REPUBLIC TO EASTERN PANAMA. AN ANTICYCLONE CENTERED
JUST E OF THE WINDWARD ISLANDS HAS A RIDGE EXTENDING WWD AND
COVERS NORTHERN SOUTH AMERICA A MOST OF THE EASTERN CARIBBEAN.

HISPANIOLA...
CURRENTLY...MOISTURE IS LIMITED OVER HISPANIOLA. A MOSTLY DRY
AND STABLE WEATHER PATTERN WILL REMAIN IN PLACE DURING MOST OF
THE WEEKEND. EXPECT ISOLATED TO SCATTERED SHOWERS AND TSTMS
DURING THE AFTERNOON AND EVENING HOURS IN ASSOCIATION WITH
DIURNAL HEATING AND LOCAL ISLAND EFFECTS. MOISTURE IS FORECAST
TO INCREASE LATE SUN INTO MON AS AN UPPER LEVEL TROUGH MOVES WWD
ACROSS THE AREA.

ATLANTIC OCEAN...
CLOUDINESS AND SHOWERS EXTENDING FROM THE NORTHWESTERN BAHAMAS
NORTHWARD ACROSS THE ATLANTIC ARE LIKELY ASSOCIATED WITH THE
REMNANTS OF CHANTAL. THIS ACTIVITY IS EXPECTED TO MOVE NORTHWARD
AND MERGE WITH A FRONTAL SYSTEM CURRENTLY LOCATED ALONG THE
EASTERN UNITED STATES DURING THE NEXT DAY. SHOWERS AND TSTMS ARE
FLARED UP OVER SOUTH-CENTRAL FLORIDA UNDER A SOUTH TO
SOUTHWESTERLY LOW LEVEL WIND FLOW. A TROUGH...REFLECTION OF AN
UPPER LEVEL LOW EXTENDS FROM 31N64W TO 24N64W. SCATTERED SHOWERS
AND TSTMS ARE ON EITHER SIDE OF THE TROUGH AXIS COVERING MAINLY
THE AREA N OF 26N BETWEEN 60W AND 68W. THIS TROUGH IS FORECAST
TO MOVE WWD REACHING NEAR 70W TONIGHT...AND NEAR 77W SUN NIGHT.
A 1024 MB HIGH PRES IS CENTERED OVER THE E ATLANTIC NEAR 31N30W
EXTENDING A RIDGE ACROSS THE E AND CENTRAL ATLC. IN THE
TROPICS...A PAIR OF TROPICAL WAVES ARE NOTED...ONE IS ALONG THE
COAST OF WEST AFRICA AND THE OTHER IS ACROSS THE CENTRAL ATLC.
SEE TROPICAL WAVES SECTION FOR MORE DETAILS. IN THE UPPER
LEVELS...AN UPPER LEVEL LOW IS SPINNING NEAR 25N61W GENERATING
SCATTERED SHOWERS AND TSTMS. SW TO W WINDS ALOFT DOMINATE MOST
OF THE AREA N OF 20N E OF 50W. SOUTH OF THESE WINDS...THERE IS
AN ANTICYCLONE CENTERED NEAR 19N29W PRODUCING MODERATE TO STRONG
SUBSIDENCE TOWARDS THE CAPE VERDE ISLANDS. AFRICAN DUST
CONTINUES TO SPREAD WWD ACROSS THE EAST-CENTRAL ATLC ON THE
HEELS OF THE TROPICAL WAVE ALONG 37W/38W. THE SAHARAN AIR LAYER
TRACKING PRODUCT CONFIRMS THE PRESENCE OF THIS DUST.

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

$$
GR


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