[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 182352
TWDAT

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

...TROPICAL WAVES...

A TROPICAL WAVE IS ALONG 32W/33W S OF 18N MOVING W NEAR 15 KT.
NO DEEP CONVECTION IS ASSOCIATED WITH THIS WAVE DUE TO THE
PRESENCE OF SAHARAN DUST TO THE NORTH AND EAST OF THE WAVE AXIS.
HOWEVER...SLIGHT LOW TO MID-LEVEL CYCLONIC TURNING IS NOTED IN
VISIBLE SATELLITE IMAGERY AND SATELLITE DERIVED WINDS.

A TROPICAL WAVE IS ALONG 45W/46W S OF 18N MOVING W NEAR 20 KT.
LOW TO MID-LEVEL CYCLONIC TURNING IS NOTED IN VISIBLE SATELLITE
IMAGERY.THIS WAVE ALSO COINCIDES WITH A LOW AMPLITUDE DEEP LAYER
MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY.
SCATTERED MODERATE CONVECTION IS FROM 11N-13N BETWEEN 46W-49W.

A TROPICAL WAVE EXTENDS FROM 21N61W TO 11N63W MOVING W NEAR 18
KT. THIS WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM
OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. RADAR IMAGERY FROM
PUERTO RICO INDICATES NE FLOW W OF THE WAVE AXIS AS IT
APPROACHES THE ISLAND FROM THE E. SCATTERED MODERATE CONVECTION
IS E OF THE WAVE AXIS FROM 12N-18N BETWEEN 56W-62W. THIS
CONVECTION IS BEING ENHANCED BY UPPER LEVEL DIFFLUENCE.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 13N12W 10N21W 11N31W 11N44W
11N61W. SCATTERED MODERATE CONVECTION IS WITHIN 150 NM S OF THE
AXIS BETWEEN 12W-20W. SIMILAR CONVECTION IS FROM 5N-8N BETWEEN
48W-53W...AND FROM 11N-13N BETWEEN 47W-49W.

...DISCUSSION...

GULF OF MEXICO...
A COLD FRONT ENTERS THE DISCUSSION AREA NEAR 31N85W CONTINUING
TO 30N89W. A SURFACE TROUGH EXTENDS FROM THE FRONT NEAR 29N88W
TO 28N94W. THIS SYSTEM IS SUPPORTED BY AN UPPER LEVEL TROUGH
OVER THE ERN CONUS FROM AN UPPER LEVEL LOW N OF THE GREAT LAKES
EXTENDING TO THE NW GULF OF MEXICO NEAR 28N95W. SURFACE
CONVERGENCE ALONG WITH UPPER LEVEL DIFFLUENCE IS GENERATING
NUMEROUS SHOWERS/THUNDERSTORMS ACROSS THE NRN GULF FROM 26N-30N
E OF 98W. AN OUTFLOW BOUNDARY IS ANALYZED AT THE LEADING EDGE OF
THE THUNDERSTORMS EXTENDING FROM 29N82W TO 26N90W. A SURFACE
RIDGE ANCHORED BY A 1020 MB SURFACE HIGH NEAR 25N89W DOMINATES
THE SRN GULF OF MEXICO S OF 26N BRINGING GENERALLY FAIR WEATHER.
SUBSIDENCE ALOFT ALONG WITH A MID-LEVEL DRY SAHARAN AIR LAYER
SUPPORT THE SURFACE RIDGE. ANTICYCLONIC FLOW AROUND THE SURFACE
RIDGE IS SUPPORTING MOSTLY E TO SE WINDS OF 10-15 KT ACROSS THE
MAJORITY OF THE SRN GULF.

CARIBBEAN SEA...
FRESH TO STRONG TRADE WINDS ARE OCCURRING BETWEEN THE
SUBTROPICAL RIDGE OVER THE CENTRAL ATLC AND A BROAD TROUGH OVER
NWRN SOUTH AMERICA...WITH THE STRONGEST FLOW NEAR THE COAST OF
COLOMBIA. THESE TRADE WINDS ARE FORECAST TO REMAIN FRESH TO
STRONG THROUGH MONDAY AS THE SUBTROPICAL RIDGE REMAINS IN PLACE.
HOWEVER...THE PROPAGATION OF A TROPICAL WAVE JUST W OF THE
LESSER ANTILLES...AND A SECOND TROPICAL WAVE THAT WILL REACH THE
ERN CARIBBEAN BY TUE WILL CAUSE THE TRADE WIND PATTERN TO
FLUCTUATE AS THE WAVES PASS THROUGH THE CARIBBEAN. HIGHEST WINDS
ARE EXPECTED TO BE MAINLY ACROSS THE N PORTIONS OF THESE
TROPICAL WAVES. THE NW CARIBBEAN N OF 16N W OF 78W IS UNDER THE
INFLUENCE OF A DRY SAHARAN AIR LAYER SUPPORTING GENERALLY FAIR
WEATHER. ISOLATED SHOWERS/THUNDERSTORMS ARE ACROSS THE REMAINDER
OF THE CARIBBEAN BECOMING SCATTERED S OF 11N BETWEEN
78W-85W...AND E OF THE TROPICAL WAVE IN THE ERN CARIBBEAN...SEE
ABOVE. UPPER LEVEL DIFFLUENCE BETWEEN A BROAD UPPER LEVEL RIDGE
THAT DOMINATES THE MAJORITY OF THE CARIBBEAN CENTERED NEAR
14N65W AND AN UPPER LEVEL LOW CENTERED OVER THE BAY OF CAMPECHE
NEAR 20N92W SUPPORTS THE SHOWER ACTIVITY.

ATLANTIC OCEAN...
SCATTERED SHOWERS/THUNDERSTORMS ARE ACROSS THE W ATLC N OF 26N W
OF 73W. UPPER LEVEL DIFFLUENCE E OF AN UPPER LEVEL TROUGH OVER
THE ERN CONUS ALONG WITH DEEP LAYER MOISTURE ARE SUPPORTING THE
SHOWER ACTIVITY. THE REMAINDER OF THE ATLC IS UNDER A BROAD
SURFACE RIDGE ANCHORED BY A PAIR OF 1032 MB SURFACE HIGHS N OF
THE DISCUSSION AREA NEAR 36N42W AND 37N31W BRINGING GENERALLY
FAIR WEATHER ACROSS THE AREA. UPPER LEVEL DIFFLUENCE BETWEEN AN
UPPER LEVEL HIGH NEAR 17N47W AND AN UPPER LEVEL LOW NEAR 29N50W
IS SUPPORTING AN AREA OF SCATTERED SHOWERS FROM 20N-25N BETWEEN
45W-58W. THE TROPICAL WAVE W OF THE LESSER ANTILLES IS MOST
LIKELY ENHANCING THESE SHOWERS. ACROSS THE TROPICAL ATLC...AN
UPPER LEVEL RIDGE IS E OF 27W SUPPORTING CONVECTION ALONG THE
ITCZ NEAR THE COAST OF AFRICA.

$$
WALTON





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