000
AXNT20 KNHC 181047
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT SAT JUL 18 2009

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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 1015 UTC.

...TROPICAL WAVES...
AN ATLANTIC OCEAN TROPICAL WAVE IS ALONG 28W TO THE SOUTH OF 
15N MOVING WESTWARD 10 KT. ANY NEARBY PRECIPITATION REALLY 
APPEARS TO BE MORE RELATED TO THE ITCZ THAN TO THE WAVE.

AN ATLANTIC OCEAN TROPICAL WAVE IS ALONG 39W/40W TO THE SOUTH OF
16N MOVING WESTWARD 10 KT. THIS WAVE COINCIDES WITH A LOW LEVEL 
TO MIDDLE LEVEL CYCLONIC CIRCULATION CENTER. IT IS NOT EASY TO 
DETERMINE THAT ANY NEARBY PRECIPITATION REALLY JUST IS RELATED 
TO THIS WAVE AND/OR TO THE ITCZ. SCATTERED MODERATE SHOWERS TO
ISOLATED STRONG THUNDERSTORMS FROM 11N TO 13N BETWEEN 42W AND 
46W.

A TROPICAL WAVE IS ALONG 58W TO THE SOUTH OF 20N MOVING WESTWARD 
15 TO 20 KT. AN UPPER LEVEL TROUGH GOES FROM 32N51W TO
A CYCLONIC CIRCULATION CENTER NEAR 28N52W TO 24N55W TO 19N59W. 
SCATTERED STRONG SHOWERS AND THUNDERSTORMS ARE FROM 15N TO 18N 
BETWEEN 56W AND 60W...AND FROM 13N TO 14N BETWEEN 60W AND 61W. 
OTHER RESIDUAL CONVECTIVE DEBRIS CLOUDS LINGER FROM 10N TO 20N 
BETWEEN 50W AND 60W.

...THE ITCZ...

FROM 10N TO 11N BETWEEN THE AFRICA COAST AND 56W...TO 11N58W
AND TRINIDAD. THE EARLIER STRONG PRECIPITATION IN THE COASTAL
WATERS OF AFRICA HAS WEAKENED BUT IT REMAINS INTACT TO SOME
DEGREE. ISOLATED MODERATE SHOWERS AND POSSIBLE THUNDERSTORMS
ARE ELSEWHERE FROM 4N TO 14N BETWEEN AFRICA AND 55W. THE
PRECIPITATION FROM SIX HOURS AGO NEAR THE BRAZIL COAST HAS
WEAKENED.

...DISCUSSION...

THE GULF OF MEXICO...
UPPER LEVEL SOUTHWESTERLY WIND FLOW COVERS THE AREA TO THE
NORTH OF 28N...IN RESPONSE TO A DIGGING TROUGH THAT EXTENDS
FROM THE U.S.A. GREAT LAKES AREA...THROUGH WESTERN KENTUCKY
AND TENNESSEE...TO EAST TEXAS. BROKEN TO OVERCAST MULTILAYERED 
CLOUDS AND ISOLATED MODERATE SHOWERS ARE IN THE COASTAL WATERS 
TO THE NORTH OF 26N. A MIDDLE LEVEL TO UPPER LEVEL TROUGH 
EXTENDS FROM THE SOUTHWESTERN CORNER OF THE GULF OF MEXICO 
ACROSS GUATEMALA INTO NORTHWESTERN HONDURAS. A FEW CELLS
OF SHOWERS AND POSSIBLE THUNDERSTORMS ARE FROM 17N TO 19N 
BETWEEN 95W AND 96W FROM THE COASTAL WATERS TO THE ISTHMUS
OF TEHUANTEPEC.

THE CARIBBEAN SEA...
A POSSIBLE REMNANT TROUGH CONTINUES FROM THE 19N59W POINT OF THE 
ATLANTIC OCEAN 32N50W-TO-19N59W TROUGH...TO 15N70W TO 10N80W IN 
THE SOUTHWESTERN CORNER OF THE AREA. ISOLATED MODERATE SHOWERS 
AND POSSIBLE THUNDERSTORMS ARE IN THE WATERS TO THE SOUTHEAST
OF THE TROUGH TO THE EAST OF 71W. A MIDDLE LEVEL TO UPPER LEVEL 
TROUGH EXTENDS FROM THE SOUTHWESTERN CORNER OF THE GULF OF 
MEXICO ACROSS GUATEMALA INTO NORTHWESTERN HONDURAS. ISOLATED 
MODERATE SHOWERS CURRENTLY ARE IN THE WATERS TO THE SOUTH OF 17N 
TO THE WEST OF 86W. MOST OF THE PRECIPITATION THAT WAS OCCURRING 
IN CENTRAL GUATEMALA HAS DISSIPATED. THE STRONG PRECIPITATION 
THAT WAS OCCURRING IN NORTHERN SOUTH AMERICA SIX HOURS AGO HAS 
DISSIPATED. THE PRECIPITATION HAD BEEN OCCURRING IN AN AREA OF 
DIRECTIONAL WIND SHEAR FROM AT LEAST 500 MB TO 200 MB ACCORDING 
TO THE GFS MODEL.

THE ATLANTIC OCEAN...
AN UPPER LEVEL TROUGH GOES FROM 32N51W TO A CYCLONIC CIRCULATION 
CENTER NEAR 28N52W TO 24N55W TO 19N59W. THIS TROUGH IS ON TOP OF 
THE AREA THROUGH WHICH THE 58W TROPICAL WAVE IS MOVING. AN UPPER 
LEVEL TROUGH EXTENDS FROM A 32N21W CYCLONIC CIRCULATION CENTER 
TO 27N22W TO 22N30W. ANOTHER BRANCH OF A TROUGH THAT MAY BE 
CONNECTED TO THE 32N21W 22N30W TROUGH IS ALONG 24N37W 18N40W 
12N43W. SCATTERED MODERATE SHOWERS TO ISOLATED STRONG 
THUNDERSTORMS FROM 11N TO 13N BETWEEN 42W AND 46W. A TROPICAL 
WAVE NOW IS ALONG 39W/40W TO THE SOUTH OF 16N. BROAD SURFACE 
ANTICYCLONIC FLOW COVERS THE AREA. A SURFACE RIDGE 26N77W 27N59W 
BEYOND 32N50W.

$$
MT