[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 182352
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT THU SEP 18 2008

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...METEOROLOGICAL ANALYSIS...WEATHER
OBSERVATIONS...AND RADAR.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...TROPICAL WAVES...
A TROPICAL WAVE IS OVER THE CAPE VERDE ISLANDS ALONG 25W S OF
17N MOVING W NEAR 10 KT. A SWIRL OF LOW CLOUDS IS NEAR 16N. ONLY
ISOLATED SHOWERS ARE SEEN NEAR THE INTERSECTION OF THE WAVE AXIS
AND THE ITCZ. THE SSMI TPW PRODUCT FROM CIMSS SHOWS A BULGE OF
MOISTURE ALONG THE WAVE AXIS.

A TROPICAL WAVE IS ALONG 46W S OF 19N MOVING WNW NEAR 10 KT.
THIS WAVE IS EMBEDDED WITHIN AN AREA OF DRY SOMEWHAT STABLE
AIR...THUS ONLY PATCHES OF LOW LEVEL MOISTURE ARE NEAR THE
NORTHERN END OF THE WAVE LINE.

A TROPICAL WAVE IS OVER THE LESSER ANTILLES ALONG 62W S OF 20N
MOVING SLOWLY WWD. THIS WAVE WAS ADDED TO THE 1200 UTC ANALYSIS
BASED ON A LONG-TERM SATELLITE LOOP. THE COMBINATION OF AN UPPER
TROUGH TO THE W OF THE WAVE AND AN UPPER RIDGE TO THE E IS
GREATLY ENHANCING THE SHOWER/TSTM ACTIVITY ASSOCIATED WITH THIS
FEATURE. LATEST SATELLITE IMAGERY INDICATES THAT CONVECTION HAS
SLIGHTLY DIMINISHED DURING THE PAST FEW HOURS. NEVERTHELESS...
THE WAVE CONTINUES TO PRODUCE A LARGE AREA OF SHOWERS AND A FEW
THUNDERSTORMS OVER THE LESSER ANTILLES. SIGNIFICANT DEVELOPMENT
OF THIS SYSTEM DOES NOT APPEAR LIKELY DURING THE NEXT COUPLE OF
DAYS AS IT MOVES SLOWLY WEST-NORTHWESTWARD...BUT LOCALLY HEAVY
RAINS COULD CONTINUE OVER PORTIONS OF THE WINDWARD AND LEEWARD
ISLANDS TONIGHT AND TOMORROW. MOISTURE ASSOCIATED WITH THIS
TROPICAL WAVE IS FORECAST BY THE COMPUTER MODELS TO SPREAD OVER
THE UK/US VIRGIN ISLANDS AND PUERTO RICO LATE FRI INTO SAT
INCREASING THE LIKELIHOOD OF SHOWERS AND TSTMS OVER THOSE
ISLANDS.

A TROPICAL WAVE IS ALONG 72W S OF 19N MOVING W 10-15 KT. THE
WAVE IS GENERATING SCATTERED MODERATE CONVECTION OVER HISPANIOLA
AS WELL AS OVER WESTERN VENEZUELA...INCLUDING THE LAKE MARACAIBO
AREA AND NORTHERN COLOMBIA. AN UPPER RIDGE JUST TO THE W OF THE
WAVE AXIS IS ENHANCING CONVECTION ASSOCIATED WITH THIS
FEATURE.

A TROPICAL WAVE IS OVER THE YUCATAN PENINSULA AND GUATEMALA WITH
THE AXIS ALONG 89W/90W S OF 22N MOVING W 10-15 KT. SCATTERED
SHOWERS AND TSTMS ARE OBSERVED ASSOCIATED WITH THE WAVE.

...THE ITCZ...
ITCZ AXIS IS ANALYZED ALONG 13N17W 12N24W 10N35W 11N50W 12N60W.
CONVECTION ALONG THE ITCZ IS CONFINED TO WEST OF 50W AND WITHIN
120 NM N OF AXIS WHERE AN AREA OF MODERATE/ISOLATED STRONG
CONVECTION IS NOTED. SIMILAR CONVECTION IS INLAND OVER SW AFRICA
COVERING THE AREA FROM 4N-10N BETWEEN 3W-11W.

...DISCUSSION...

GULF OF MEXICO...
A WEAK STATIONARY FRONT REMAINS OVER THE GULF AND EXTENDS FROM
NEAR TAMPA BAY FLORIDA WWD TO 27N93W...THEN CONTINUES SWD ALONG
94W TO THE BAY OF CAMPECHE AND ALONG THE ISTHMUS OF TEHUANTEPEC.
A 1012 MB FRONTAL LOW IS NEAR 22N95W. ABUNDANT CLOUDINESS WITH
EMBEDDED SHOWERS AND ISOLATED TSTMS IS ASSOCIATED WITH THIS
FRONTAL SYSTEM OVER THE WESTERN GULF MAINLY S OF 27N. AN EARLIER
ASCAT PASS SHOWED NWLY WINDS OF 20 TO 25 KT JUST BEHIND THE
FRONT OVER THE BAY OF CAMPECHE. THE CITY OF VERACRUZ MEXICO HAS
BEEN REPORTED LIGHT RAIN AND SUSTAINED WINDS UP TO 18 KT TODAY.
A DEEP LAYERED TROUGH ALONG THE E COAST OF U.S. SUPPORTS THIS
FRONT. THE UPPER-LEVEL TROUGH DIPS SOUTH INTO THE EASTERN GULF
AND THE STATE OF FLORIDA. THE REMAINDER OF THE GULF REGION IS
UNDER THE INFLUENCE OF AN UPPER-LEVEL HIGH CENTERED NEAR
VERACRUZ. THIS UPPER-LEVEL FEATURE IS ENHANCING CONVECTION ALONG
THE FRONTAL BOUNDARY. WV IMAGERY INDICATES SUBSIDENCE/DRY AIR
ACROSS THE SE CONUS DROPPING S INTO THE FLORIDA PENINSULA TO
NEAR LAKE OKEECHOBEE. SOME OF THIS DRIER AIR IS FORECAST TO
REACH SOUTH FLORIDA TOMORROW. INSTABILITY NEAR THE TROUGH AXIS
IS PRODUCING ISOLATED SHOWERS AND THUNDERSTORMS OVER THE FAR NE
GULF. THE SURFACE LOW IS EXPECTED TO DRIFT NORTHWARD AS THE
FRONT BEGINS TO DISSIPATE INTO THE WEEKEND.

CARIBBEAN SEA...
THREE TROPICAL WAVES ARE BETWEEN THE LESSER ANTILLES AND THE
YUCATAN PENINSULA. SEE TROPICAL WAVE SECTION FOR DETAILS. A
HUMID AND UNSTABLE ATMOSPHERE PREVAILS ACROSS MOST OF THE BASIN
DUE TO THE TROPICAL WAVES AND FAVORABLE UPPER LEVEL CONDITIONS.
DIFFLUENCE IN NORTHERLY FLOW ALOFT IS HELPING TO INDUCE SEVERAL
CLUSTERS OF MODERATE/ISOLATED STRONG CONVECTION OVER CENTRAL
AMERICA AND THE SW CARIBBEAN...PARTICULARLY SOUTH OF 15N
INCLUDING ALSO PARTS OF PANAMA AND COSTA RICA. FURTHERMORE...AN
UPPER-LEVEL TROUGH EXTENDS FROM AN UPPER-LEVEL LOW LOCATED N OF
PUERTO RICO INTO THE E CARIBBEAN ALONG 66W/67W. THE TROPICAL
WAVE ALONG 62W...THAT APPEARS TO BE THE MOST SIGNIFICANT FEATURE
IN THE REGION...IS INTERACTING WITH THIS UPPER-LEVEL TROUGH. AN
UPPER LEVEL HIGH IS JUST EAST OF THE LESSER ANTILLES NEAR 14N59W
COVERING THE FAR E CARIBBEAN. CONVECTION HAS ALSO FLARE UP OVER
CUBA AND HISPANIOLA. MODERATE TRADE WINDS ARE BLOWING ACROSS THE
REGION...BUT WINDS AND SEAS ARE EXCEPTED TO BE HIGHER NEAR THE
AREAS OF TSTMS.

ATLANTIC OCEAN...
A FRONTAL BOUNDARY ENTERS THE AREA NEAR 31N75W THEN CONTINUES SW
ACROSS NORTH-CENTRAL FLORIDA INTO THE GULF OF MEXICO. SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS ARE RELATED TO THE FRONT.
SIMILAR ACTIVITY IS NOTED OVER THE BAHAMAS AHEAD OF THE
AFOREMENTIONED UPPER-LEVEL TROUGH WHICH SUPPORTS THE FRONT AND
EXTENDS ALONG THE EASTERN SEABOARD. FURTHER EAST...AN UPPER-
LEVEL LOW LOCATED NEAR 23N68W CONTINUES TO GENERATE SCATTERED
MODERATE CONVECTION WITHIN 180 NM NE QUADRANT OF THE LOW CENTER.
ACROSS THE TROPICAL ATLC THERE IS A COUPLE OF TROPICAL WAVE. N
OF 20N...A SURFACE RIDGE DOMINATES THE FORECAST REGION BRINGING
MOSTLY FAIR WEATHER TO MUCH OF THE AREA. AN UPPER LEVEL LOW IS
OVER THE CENTRAL ATLC NEAR 22N42W PRODUCING SOME CLOUDINESS AND
ISOLATED SHOWERS. A 1011 SURFACE LOW IS SW OF THE MADEIRA
ISLANDS NEAR 32N20W. SCATTERED SHOWERS ARE ASSOCIATED WITH THIS
SFC LOW AND AN UPPER-LEVEL LOW SPINNING JUST SW OF THE SFC LOW
NEAR 31N22W. THE TYPICAL LARGE E/W UPPER LEVEL RIDGE IS ACROSS
THE REMAINDER OF THE TROPICAL ATLC LIMITING CONVECTION ALONG THE
ITCZ.

$$
GR



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