[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 212358
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT TUE JUL 21 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...TROPICAL WAVES...

A TROPICAL WAVE EXTENDS FROM 13N39W TO 7N41W TO 3N41W MOVING W
20-25 KT. THIS WAVE COINCIDES WITH A WEAK MAXIMUM IN LOW LEVEL
CYCLONIC CIRCULATION BASED ON THE CIMSS WAVETRAK PRODUCT.
CONFLUENT SOUTHEASTERLY FLOW IN THE UPPER LEVELS AND THE
PRESENCE OF DRY LOW/MID-LEVEL SAHARAN AIR ARE INHIBITING THE
AREAL COVERAGE OF DEEP CONVECTION NEAR THE WAVE. HOWEVER...
SCATTERED MODERATE CONVECTION IS FROM 7N-9N BETWEEN 40W-42W.

A TROPICAL WAVE IS ALONG 59W/60W S OF 22N MOVING W NEAR 25 KT.
THIS WAVE COINCIDES WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED
ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. THIS WAVE IS
FOLLOWED BY ABUNDANT DRY LOW/MID-LEVEL SAHARAN AIR...WHICH IS
INHIBITING THE AREAL COVERAGE OF DEEP CONVECTION NEAR THE WAVE.
HOWEVER...SCATTERED MODERATE CONVECTION IS FROM 8N-10N BETWEEN
58W-60W.

A TROPICAL WAVE IS ALONG 70W S OF 22N MOVING W 20-25 KT. THE
INVERTED SURFACE TROUGH ASSOCIATED WITH THIS WAVE IS NOT AS
AMPLIFIED AS IT WAS YESTERDAY BASED ON MEAN SEA LEVEL PRESSURE
ANALYSIS OVER THE CARIBBEAN. NEVERTHELESS...SURFACE OBSERVATIONS
ACROSS THE E CARIBBEAN INDICATE WINDS WITH A NORTHEASTERLY
COMPONENT AHEAD OF THE WAVE AND WINDS WITH A SOUTHEASTERLY
COMPONENT BEHIND THE WAVE. THIS WAVE IS ENHANCING NUMEROUS
MODERATE/SCATTERED STRONG CONVECTION OVER THE N CENTRAL
CARIBBEAN AND SOUTHERN PORTIONS OF THE SW NORTH ATLC FROM
15N-23N BETWEEN 63W-75W. LOCALLY HEAVY RAINFALL AND GUSTY WINDS
ASSOCIATED WITH THE CONVECTION WILL AFFECT PORTIONS OF THE
VIRGIN ISLANDS...PUERTO RICO...THE DOMINICAN REPUBLIC...AND
HAITI THROUGH TONIGHT.

A TROPICAL WAVE IS ALONG 87W S OF 20N MOVING W NEAR 20 KT.
RECENT SATELLITE IMAGERY INDICATES THAT THIS WAVE COINCIDES WITH
A BROAD AREA OF LOW/MID-LEVEL CYCLONIC CIRCULATION OVER PORTIONS
OF THE SW CARIBBEAN AND E PACIFIC REGION. THIS WAVE IS
ASSOCIATED WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED ON THE
TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS FROM 9N-16N BETWEEN
81W-87W...WHICH IS BEING ENHANCED BY ATMOSPHERIC INSTABILITY
DRIVEN BY DIURNAL HEATING OVER CENTRAL AMERICA.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 15N17W 14N26W 10N35W 6N47W
7N59W. SCATTERED MODERATE CONVECTION IS FROM 8N-11N BETWEEN
44W-48W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM
4N-8N BETWEEN 49W-55W.

...DISCUSSION...

GULF OF MEXICO...
A SHARP UPPER LEVEL TROUGH EXTENDS FROM THE E UNITED STATES
SOUTHWARD OVER THE FLORIDA PENINSULA. ATMOSPHERIC INSTABILITY
ASSOCIATED WITH THIS TROUGH IS SUPPORTING SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS ACROSS THE SE GULF S OF 26N E OF 85W.
THIS ACTIVITY IS BEING ENHANCED BY LOW LEVEL CONVERGENCE NEAR A
WEAK SURFACE TROUGH EXTENDING FROM 25N85W TO THE W FLORIDA
PENINSULA NEAR 27N82W. ACROSS THE REMAINDER OF THE
GULF...SUBSIDENCE IN NORTHWESTERLY FLOW ALOFT TO THE W OF THE
UPPER LEVEL TROUGH IS SUPPORTING A SURFACE RIDGE ACROSS THE N
GULF...ALONG WITH GENERALLY FAIR WEATHER. HOWEVER...HIGH LEVEL
CLOUDS FROM SHOWER AND THUNDERSTORM ACTIVITY OVER TEXAS ARE
BEING ADVECTED SOUTHEASTWARD ACROSS THE NW GULF. THIS ACTIVITY
IS BEING SUPPORTED BY A WEAK SHORTWAVE TROUGH EMBEDDED WITHIN
NORTHWESTERLY FLOW ALOFT. THE SURFACE RIDGE IS FORECAST TO
PERSIST ACROSS THE N GULF THROUGH THIS WEEKEND WITH E TO SE
RETURN FLOW ACROSS MUCH OF THE GULF THROUGH THIS WEEKEND.

CARIBBEAN SEA...
A BROAD UPPER LEVEL ANTICYCLONE IS OVER THE W CARIBBEAN...
CENTERED NEAR 14N80W. UPPER LEVEL DIFFLUENCE ASSOCIATED WITH
THIS ANTICYCLONE IS SUPPORTING SCATTERED SHOWERS AND
THUNDERSTORMS ACROSS THE SW CARIBBEAN S OF 12N BETWEEN
75W-79W...AS WELL AS THE CONVECTION ASSOCIATED WITH THE TROPICAL
WAVE IN THE W CARIBBEAN ALONG 87W S OF 20N. THE UPPER LEVEL
DIFFLUENCE IS ALSO SUPPORTING SCATTERED SHOWERS AND
THUNDERSTORMS OVER CUBA AND JAMAICA...WHERE ATMOSPHERIC
INSTABILITY IS BEING ENHANCED BY DIURNAL HEATING. ACROSS THE E
CARIBBEAN...AN UPPER LEVEL TROUGH IS PRESENT. ATMOSPHERIC
INSTABILITY NEAR THIS TROUGH...AND UPPER LEVEL DIFFLUENCE
BETWEEN THIS TROUGH AND AN UPPER LEVEL RIDGE OVER THE TROPICAL
NORTH ATLC...ARE SUPPORTING THE CONVECTION ASSOCIATED WITH THE
TROPICAL WAVE IN THE E CARIBBEAN ALONG 70W S OF 22N. THESE
TROPICAL WAVES ARE INTERACTING WITH A SURFACE RIDGE N OF THE
CARIBBEAN TO RESULT IN FRESH TO STRONG WINDS ACROSS THE E AND
CENTRAL CARIBBEAN. THESE FRESH TO STRONG WINDS WILL CONTINUE
ACROSS THE E AND CENTRAL CARIBBEAN THROUGH THE REMAINDER OF THIS
WEEK.

ATLANTIC OCEAN...
A SHARP UPPER LEVEL TROUGH EXTENDS FROM THE E UNITED STATES
SOUTHWARD OVER THE FLORIDA PENINSULA. THIS TROUGH IS ASSOCIATED
WITH SURFACE TROUGHS EXTENDING FROM 25N79W TO 31N78W AND FROM
31N76W TO 32N75W TO NE OF THE DISCUSSION AREA. STRONG UPPER
LEVEL DIFFLUENCE IN MOIST SOUTHWESTERLY FLOW ALOFT BETWEEN THE
UPPER LEVEL TROUGH AND AN UPPER LEVEL RIDGE FARTHER TO THE E IS
SUPPORTING NUMEROUS SHOWERS AND SCATTERED THUNDERSTORMS N OF 21N
W OF 68W. THIS ACTIVITY IS ALSO BEING ENHANCED BY LOW LEVEL
CONVERGENCE NEAR THE SURFACE TROUGHS AND NEAR N PORTIONS OF THE
TROPICAL WAVE ALONG 70W S OF 22N. THE SURFACE PRESSURE GRADIENT
E OF THE SURFACE TROUGHS IS SUPPORTING E TO SE WINDS OF 20 TO 25
KT FROM 17N-25N BETWEEN 60W-75W BASED ON THE ASCAT PASS AROUND
21/1510 UTC AND GLOBAL MODEL GUIDANCE. FARTHER TO THE E...
SUBSIDENCE ASSOCIATED WITH A SURFACE RIDGE IS RESULTING IN
GENERALLY FAIR WEATHER ACROSS MUCH OF THE CENTRAL AND E ATLC.
THIS SURFACE RIDGE IS ASSOCIATED WITH A 1030 MB SURFACE HIGH
NEAR 37N58W. HOWEVER...A SURFACE TROUGH OVER THE E ATLC EXTENDS
FROM A 1014 MB SURFACE LOW NEAR 22N20W TO 17N24W. LOW LEVEL
CONVERGENCE IS SUPPORTING SCATTERED SHOWERS WITHIN 60 NM EITHER
SIDE OF THIS SURFACE TROUGH. ACROSS THE TROPICAL ATLC...
ATMOSPHERIC INSTABILITY AND UPPER LEVEL DIFFLUENCE ASSOCIATED
WITH A SHORTWAVE TROUGH EMBEDDED WITHIN EASTERLY UPPER LEVEL
FLOW IS SUPPORTING THE CONVECTION ASSOCIATED WITH THE ITCZ
BETWEEN 44W-55W.

$$
COHEN




This weather bulletin was brought to you by:
www.nashvilleweather.net