Tropical Weather Discussion
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000
AXNT20 KNHC 270007
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT WED AUG 26 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
2345 UTC.

...SPECIAL FEATURES...

TROPICAL STORM ERIKA IS CENTERED NEAR 16.6N 58.9W AT 26/2100 UTC
OR ABOUT 170 NM E OF ANTIGUA...MOVING W AT 15 KT. ESTIMATED
CENTRAL PRESSURE IS 1005 MB. MAXIMUM SUSTAINED WIND SPEED IS 40
KT WITH GUSTS TO 50 KT. NUMEROUS MODERATE TO ISOLATED STRONG
CONVECTION IS FROM 13N TO 17N BETWEEN 55W AND 59W. SCATTERED
MODERATE CONVECTION IS ELSEWHERE FROM 12N TO 19N BETWEEN 54W AND
60W. PLEASE SEE THE LATEST FORECAST/ADVISORY UNDER AWIPS/WMO
HEADERS MIATCMAT5/WTNT25 KNHC FOR MORE DETAILS.

...TROPICAL WAVES...

A TRPCL WAVE CAME OFF THE WEST AFRICAN COAST EARLIER THIS
AFTERNOON. ITS AXIS IS APPROXIMATELY ALONG 18W AND IS EXPECTED
TO MOVE W AT 10-15 KT WITHIN THE NEXT 48 HOURS. MODERATE
MOISTURE IS ASSOCIATED WITH THIS WAVE FROM THE SURFACE TO 850 MB
AS INDICATED BY CIRA LAYER PRECIPITABLE WATER IMAGERY. LOW-LEVEL
MOISTURE CONVERGENCE SUPPORTS ISOLATED SHOWERS AND TSTMS FROM
07N TO 14N BETWEEN 18W AND 25W. FURTHER CONVECTION IS BEING
HINDERED BY THE PRESENCE OF SAHARAN DRY AIR AND DUST IN THE
NORTHERN WAVE ENVIRONMENT.

A TROPICAL WAVE IS OVER THE CENTRAL ATLANTIC WITH AXIS NEAR
36W...MOVING W AT 15 KT DURING THE PAST 24 HOURS. A BROAD AREA
OF MODERATE MOISTURE IS ASSOCIATED WITH THIS WAVE FROM THE
SURFACE TO NEARLY 700 MB AS INDICATED BY CIRA LAYER PRECIPITABLE
WATER IMAGERY. THIS IMAGERY ALSO SHOWS A TONGUE OF DRY AIR
WRAPPING THE WAVE ENVIRONMENT...WHICH COINCIDES WITH THE
PRESENCE OF SAHARAN DRY AIR AND DUST ACCORDING TO ENHACEMENTS OF
METEOSAT IMAGERY. NO CONVECTION IS OBSERVED AT THIS TIME.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH AXIS EXTENDS W OF A TROPICAL WAVE FROM 10N20W
TO 09N32W TO 08N39W. THE ITCZ BEGINS NEAR 08N39W AND CONTINUES
TO 08N50W. ASIDE THE CONVECTION ASSOCIATED WITH THE WAVE E OF
THE CAPE VERDE ISLANDS...ISOLATED SHOWERS ARE FROM 03N TO 11N
BETWEEN 23W AND 37W.

...DISCUSSION...

GULF OF MEXICO...

A BROAD MIDDLE TO UPPER-LEVEL TROUGH EXTENDS FROM THE OHIO
VALLEY S-SW ACROSS THE GULF TO A BASE OVER THE YUCATAN
PENINSULA. THIS TROUGH SUPPORTS A FRONTAL SYSTEM ANALYZED AS
STATIONARY FROM A 1010 MB LOW OVER SOUTH CAROLINA ACROSS
NORTHERN FLORIDA TO 29N82W TO 24N90W TO 24N94W. THE UPPER TROUGH
ALSO SUPPORT A PAIR OF SURFACE TROUGHS...ONE AHEAD OF THE FRONT
ALONG THE FLORIDA PENINSULA AND A SECOND TROUGH W OF THE FRONT
TAIL FROM 24N96W TO 18N94W. MOISTURE ADVECTION FROM THE
CARIBBEAN IS CONVERGING WITH MOISTURE ASSOCIATED WITH THE FRONT
GENERATING INSTABILITY THAT ALONG WITH A DIVERGENT ENVIRONMENT
ALOFT SUPPORT HEAVY SHOWERS AND TSTMS OVER THE SW GULF S OF 25N
W OF 91W. SIMILAR CONVECTION ASSOCIATED WITH THE TROUGH ALONG
FLORIDA EXTENDS OVER SE GULF WATERS FROM 25N TO 26N E OF 83W.
DRY AIR SUBSIDENCE AND STRONG DEEP LAYER WIND SHEAR N OF THE
FRONT SUPPORT FAIR WEATHER N OF 26N. NORTHERLY WIND FLOW OF OF
LESS THAN 15 KT COVERS THE BASIN. A LOW PRESSURE CENTER IS
FORECAST TO DEVELOP OVER THE NE GULF ASSOCIATED WITH THE
STATIONARY FRONT THAT IS EXPECTED TO DISSIPATE BY FRIDAY.

CARIBBEAN SEA...

AN ELONGATED UPPER LOW EXTENDS FROM THE CENTRAL BAHAMAS S-SW TO
PANAMA COASTAL WATERS...WHICH ALONG WITH SHALLOW MOISTURE IN THE
CENTRAL AND WESTERN GULF SUPPORT SCATTERED MODERATE CONVECTION
AND TSTMS ALONG CUBA AND ADJACENT SOUTHERN WATERS...SOUTHERN AND
WESTERN JAMAICA AND SW CARIBBEAN S OF 14N W OF 78W. A SURFACE
TROUGH...REMNANTS OF DANNY...CONTINUE TO ENHANCE SCATTERED
SHOWERS AND TSTMS ALONG HAITI AND NORTHERN COASTAL WATERS AND
ISOLATED SHOWERS AND TSTMS OVER CENTRAL AND WESTERN DOMINICAN
REPUBLIC. ISOLATED SHOWERS CONTINUE ACROSS THE WINDWARD ISLANDS
ASSOCIATED WITH THE PROXIMITY OF TROPICAL STORM ERIKA. SEE
SPECIAL FEATURES FOR DETAILS. THE PASSAGE OF ERIKA THROUGH THE
NE CARIBBEAN THU WILL SUPPORT HEAVY SHOWERS AND POSSIBLE TSTMS
ACROSS THE LEEWARD ISLANDS...PUERTO RICO AND ADJACENT WATERS.

...HISPANIOLA...

THE REMNANTS OF DANNY IN THE FORM OF A SURFACE TROUGH CONTINUE
TO ENHANCE SCATTERED SHOWERS AND TSTMS ALONG HAITI AND NORTHERN
COASTAL WATERS AND ISOLATED SHOWERS AND TSTMS OVER CENTRAL AND
WESTERN DOMINICAN REPUBLIC. TROPICAL STORM ERIKA CURRENTLY
LOCATED E OF THE LEEWARD ISLANDS WILL MOVE N OF THE ISLAND
FRIDAY. SHOWERS ASSOCIATED WITH THE CYCLONE ARE EXPECTED TO
START THU AFTERNOON AND CONTINUE THROUGH SATURDAY...HEAVIEST
SHOWERS EXPECTED FRIDAY AS THE CENTER OF THE SYSTEM MOVES N OF
THE ISLAND OVER SW N ATLC WATERS.

ATLANTIC OCEAN...

THE MAIN FEATURE IN THE ATLC IS T.S. ERIKA DISCUSSED IN SPECIAL
FEATURE. SEE ABOVE. A BROAD MIDDLE TO UPPER-LEVEL TROUGH EXTENDS
FROM THE OHIO VALLEY S-SW ACROSS THE GULF TO A BASE OVER THE
YUCATAN PENINSULA. THIS TROUGH SUPPORTS A FRONTAL SYSTEM
ANALYZED AS STATIONARY FROM A 1010 MB LOW OVER SOUTH CAROLINA
ACROSS NORTHERN FLORIDA FROM 30N81W TO 28N82W THE ACROSS THE
CENTRAL GULF OF MEXICO. MOISTURE ADVECTION FROM THE SW N ATLC IS
CONVERGING WITH MOISTURE ASSOCIATED WITH THE FRONT GENERATING
INSTABILITY THAT ALONG WITH A DIVERGENT ENVIRONMENT ALOFT
SUPPORT HEAVY SHOWERS AND TSTMS N OF 24N W OF 75W. SIMILAR
CONVECTION IS OVER HAITI NORTHERN WATERS. OTHERWISE...SURFACE
RIDGING AND FAIR WEATHER DOMINATE ELSEWHERE.

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

$$
NR


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