[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 182358
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT THU AUG 18 2011

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 FEATURE...
THE TROPICAL WAVE IN THE W CARIBBEAN EXTENDS FROM 18N81W TO
12N80W. A WELL DEFINED MID LEVEL CYCLONIC CIRCULATION IS ALONG
THE WAVE AXIS NEAR 16N. SCATTERED MODERATE/ISOLATED STRONG
CONVECTION IS FROM 14N-17N BETWEEN 78W-82W. A LOW LEVEL
CIRCULATION IS BECOMING BETTER DEFINED AND A SURFACE LOW COULD
BE FORMING ABOUT 90 NM ENE OF CAPE GRACIAS A DIOS NICARAGUA.
ENVIRONMENTAL CONDITIONS REMAIN CONDUCIVE FOR A TROPICAL
DEPRESSION TO FORM AS LONG AS THE DISTURBANCE REMAINS OFFSHORE.
THIS SYSTEM HAS A HIGH CHANCE OF BECOMING A TROPICAL CYCLONE
BEFORE IT MOVES INLAND OVER CENTRAL AMERICA. TROPICAL STORM
CONDITIONS ARE POSSIBLE ALONG THE COASTS OF HONDURAS...THE BAY
ISLANDS...GUATEMALA AND BELIZE DURING THE NEXT DAY OR TWO AS THE
SYSTEM MOVES GENERALLY WESTWARD AT 9-13 KT.

A TROPICAL WAVE WAS INTRODUCED ON THE 18/1800 UTC MAP ALONG THE
COAST OF W AFRICA NEAR 16W FROM 13N-21N. A BROAD MID LEVEL
CYCLONIC CIRCULATION COVERS THE AREA FROM 8N-16N E OF 22W TO
INLAND OVER W AFRICA. THIS WAVE IS ALREADY SHOWING SIGNS OF
ORGANIZATION WITH A STRONG SURFACE CYCLONIC CIRCULATION
DEVELOPING ON THE SOUTHERN EXTENT OF THIS TROPICAL WAVE.
SCATTERED/NUMEROUS STRONG CONVECTION IS WITHIN 75 NM ALONG A
LINE FROM 12N19W 14N19W TO INLAND OVER SENEGAL NEAR DAKAR.
CLUSTERS OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION COVER
THE AREA FROM 8N-13N BETWEEN 17W-25W. UPPER LEVEL WINDS ARE
FORECAST TO BE CONDUCIVE FOR FURTHER DEVELOPMENT DURING THE NEXT
COUPLE OF DAYS. THIS SYSTEM HAS A MEDIUM CHANCE OF BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES
WEST-NORTHWESTWARD AT 10 TO 15 MPH.  REGARDLESS OF
DEVELOPMENT...LOCALLY HEAVY RAIN AND STRONG GUSTY WINDS ARE
POSSIBLE IN THE CAPE VERDE ISLANDS FRIDAY INTO SATURDAY.

...TROPICAL WAVES...

TROPICAL WAVE IN THE CENTRAL TROPICAL ATLC EXTEND FROM 19N43W
ALONG 15N43W TO JUST N OF THE MONSOON TROUGH NEAR 13N41W MOVING
W 15-20 KT. THIS WAVE IS WELL DEFINED IN THE LOWER LEVELS
COVERING A BROAD AREA AND BECOMING TILTED NW/SE. WAVE REMAINS
EMBEDDED WITHIN A SURGE OF DEEP LAYER MOISTURE. SCATTERED
SHOWERS ARE FROM 13N-17N BETWEEN 40W-46W.

...THE ITCZ/THE MONSOON TROUGH...

THE DEPICTION ON THE SURFACE ANALYSIS HAS A SPLIT MONSOON TROUGH
ALONG 16W AS A RESULT OF A VERY ACTIVE TROPICAL WAVE MOVING OFF
THE COAST OF AFRICA...SEE SPECIAL FEATURES ABOVE. ONE PORTION OF
THE MONSOON TROUGH EXTENDS ACROSS AFRICA. THE OTHER PORTION OF
THE MONSOON TROUGH EXTENDS FROM A DEVELOPING CIRCULATION
ASSOCIATED WITH THIS TROPICAL WAVE INTO THE TROPICAL ATLC NEAR
13N17W ALONG 15N31W RUNNING JUST S OF THE TROPICAL WAVE NEAR
12N41W TO 9N48W. THE ITCZ AXIS CONTINUES FROM 9N48W ALONG 10N55W
TO SOUTH AMERICA NEAR 10N62W. SCATTERED MODERATE/ISOLATED STRONG
CONVECTION IS WITHIN 150 NM S OF THE MONSOON TROUGH BETWEEN
43W-48W. SMALL CLUSTERS OF SCATTERED MODERATE CONVECTION DOT THE
AREA FROM 5N-10N BETWEEN 25W-37W.

...DISCUSSION...

GULF OF MEXICO...
BROAD UPPER RIDGE DOMINATES THE GULF N OF 24N ANCHORED OVER
CENTRAL TEXAS. AN INVERTED UPPER TROUGH IS OVER THE BAY OF
CAMPECHE EXTENDING FROM THE ISTHMUS OF TEHUANTEPEC TO THE N
COAST OF THE YUCATAN PENINSULA NEAR MERIDA GENERATING SCATTERED
SHOWERS AND POSSIBLE ISOLATED THUNDERSTORMS INLAND ALONG THE
COAST OF MEXICO. UPPER LEVEL CONVERGENCE IS GENERATING SCATTERED
SHOWERS/ISOLATED THUNDERSTORMS OVER THE W GULF FROM 24N-26N
BETWEEN 92W-96W. A SURFACE TROUGH EXTENDS FROM S GEORGIA THEN
INTO THE GULF NEAR TALLAHASSEE ALONG 27N85W 24N88W TO 24N92W.
AFTERNOON SHOWERS/THUNDERSTORMS HAVE DEVELOPED INLAND OVER THE
FLORIDA PENINSULA AND SE LOUISIANA WITH SOME ISOLATED SHOWERS
MOVING TO ALONG THE IMMEDIATE COASTLINES AND OVER THE FLORIDA
KEYS. THIS SURFACE TROUGH EFFECTIVELY SPLITS THE SURFACE RIDGE
FROM THE W ATLC WITH A 1016 MB HIGH OVER THE W GULF NEAR 27N95W.
WEAK SURFACE RIDGE WILL PREVAIL OVER THE N GULF THROUGH MON. A
TROPICAL WAVE IS EXPECTED TO MOVE ACROSS THE BAY OF CAMPECHE SUN
AND MON.

CARIBBEAN SEA...
THE PRIMARY CONCERN THIS EVENING IS THE POTENTIAL FOR TROPICAL
FORMATION ASSOCIATED WITH THE TROPICAL WAVE IN THE W
CARIBBEAN...SEE SPECIAL FEATURES ABOVE. THIS FEATURE IS
DOMINATING THE CARIBBEAN AND IS GENERATING ADDITIONAL SCATTERED
SHOWERS/ISOLATED THUNDERSTORMS COVERING THE AREA BETWEEN
75W-86W. AN UPPER LEVEL RIDGE COVERS THE CARIBBEAN W OF 73W
ANCHORED NEAR THE CAYMAN ISLANDS. A LARGE UPPER TROUGH IN THE
CENTRAL ATLC EXTENDS S OVER THE NE CARIBBEAN GENERATING
SCATTERED SHOWERS AND POSSIBLE ISOLATED THUNDERSTORMS FROM N OF
15N BETWEEN 70W-75W LEAVING THE REMAINDER OF THE CARIBBEAN UNDER
MOSTLY CLEAR SKIES THIS EVENING. A SURFACE LOW IS EXPECTED TO
DEVELOP ALONG THE CARIBBEAN TROPICAL WAVE WITH THE POSSIBILITY
OF TROPICAL CYCLONE FORMATION...SEE SPECIAL FEATURES ABOVE. THE
LOW WILL THEN MOVE W THROUGH THE GULF OF HONDURAS FRI AFTERNOON
TO INLAND OVER BELIZE SAT NIGHT. A TROPICAL WAVE IN THE CENTRAL
ATLC WILL ENTER THE NE CARIBBEAN SUN TO THE CENTRAL CARIBBEAN ON
TUE.

ATLANTIC OCEAN...
A SHORTWAVE UPPER TROUGH EXTENDS ALONG THE CAROLINA COAST INTO
THE W ATLC THEN THROUGH 32N78W TO NEAR GRAND BAHAMA ISLAND
GENERATING SCATTERED SHOWERS/ISOLATED THUNDERSTORMS WITHIN 120
NM OF LINE FROM OVER W CUBA NEAR SANTA CLARA ACROSS THE BAHAMAS
TO NEAR 32N74W. A LARGE UPPER LEVEL TROUGH COVERS THE REMAINDER
OF THE W ATLC AND INTO THE CENTRAL ATLC EXTENDING FROM BEYOND
32N55W THEN THROUGH AN UPPER LOW NEAR 26N57W ACROSS HISPANIOLA/
PUERTO RICO INTO THE NE CARIBBEAN. SCATTERED SHOWERS AND
POSSIBLE ISOLATED THUNDERSTORMS ARE WITHIN 120 NM OF LINE FROM
27N60W TO 32N55W. LOW LEVEL SPEED CONVERGENCE AND AN ABUNDANCE
OF DEEP LAYER MOISTURE IS GENERATING SCATTERED SHOWERS AND
POSSIBLE ISOLATED THUNDERSTORMS E OF THE LESSER ANTILLES FROM
11N-15N BETWEEN 57W AND THE LESSER ANTILLES. THE REMAINDER OF
THE ATLC BASIN IS DOMINATED BY A SURFACE RIDGE THAT EXTENDS FROM
A 1025 MB HIGH OVER THE AZORES THROUGH A 1022 MB HIGH NEAR
33N59W TO THE FLORIDA COAST NEAR DAYTONA BEACH LEAVING THE
REMAINDER OF THE ATLC UNDER FAIR CONDITIONS THIS EVENING. TWO
AREAS OF SAHARAN DRY AIR ARE ACROSS THE ATLC BASIN. THE LARGEST
S ACROSS THE TROPICAL ATLC FROM 15N-30N E OF 57W. THE SECOND IS
SMALLER N OF THE E CARIBBEAN FROM 20N-28N BETWEEN 63W-70W. THE W
ATLC SURFACE RIDGE WILL GRADUALLY WEAKEN SAT THROUGH MON.

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

$$
PAW





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