[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 171107
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT FRI JUL 17 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 1045 UTC.

...TROPICAL WAVES...
A TROPICAL WAVE IS ALONG 33W S OF 18N MOVING W NEAR 10 KT. THIS
WAVE COINCIDES WITH LOW TO MIDDLE LEVEL CYCLONIC CIRCULATION
BASED ON RECENT SATELLITE IMAGERY. THE QUIKSCAT PASS AROUND
16/2045 UTC INDICATED CYCLONIC CURVATURE IN THE FLOW NEAR THE
SURFACE IN THE VICINITY OF THIS WAVE. SCATTERED MODERATE
CONVECTION IS FROM 8N-14N BETWEEN 31W-36W.

A TROPICAL WAVE IS ALONG 52W/53W S OF 18N MOVING W NEAR 15 KT.
THIS WAVE COINCIDES WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED
ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. RECENT
SATELLITE IMAGERY INDICATES THAT THIS WAVE COINCIDES WITH AN
INVERTED-V PATTERN IN THE COVERAGE OF LOW LEVEL CLOUDS. THE
PRESENCE OF DRY LOW/MID-LEVEL SAHARAN AIR IS LIMITING DEEP
CONVECTION NEAR THIS WAVE. HOWEVER...SCATTERED MODERATE
CONVECTION IS FROM 10N-16N BETWEEN 48W-54W

A TROPICAL WAVE EXTENDS FROM THE YUCATAN PENINSULA NEAR 21N88W
TO S GUATEMALA NEAR 15N90W INTO THE E PACIFIC REGION NEAR 4N91W
MOVING W 20-25 KT. THIS WAVE IS ASSOCIATED WITH A DISTINCT AND
NARROW MAXIMUM IN TOTAL PRECIPITABLE WATER. THE WAVE IS LEADING
AN AREA OF ABUNDANT DRY LOW/MID-LEVEL SAHARAN AIR ACROSS MUCH OF
THE CENTRAL AND E CARIBBEAN. THE DRY AIR...ALONG WITH STABLE
ATMOSPHERIC CONDITIONS BENEATH AN UPPER LEVEL RIDGE OVER THE
CENTRAL AND E CARIBBEAN...ARE LIMITING THE AREAL COVERAGE OF
DEEP CONVECTION NEAR THE WAVE. HOWEVER...SCATTERED MODERATE
CONVECTION IS FROM 15N-18N BETWEEN 87W-90W INCLUDING PORTIONS OF
BELIZE...E GUATEMALA...AND THE GULF OF HONDURAS.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 13N16W 11N27W 10N39W 11N50W
9N61W. SCATTERED MODERATE CONVECTION IS FROM 7N-15N BETWEEN
19W-22W. SCATTERED MODERATE CONVECTION IS ALSO FROM 10N-14N
BETWEEN 25W-28W...WHICH IS BEING SUPPORTED BY LOW LEVEL
CONVERGENCE NEAR A SURFACE TROUGH EXTENDING FROM 15N24W TO
11N25W TO 8N24W. SCATTERED MODERATE CONVECTION IS FROM 7N-9N
BETWEEN 39W-43W.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER LEVEL RIDGE IS PRESENT ACROSS THE NE GULF...WITH A
SURFACE RIDGE ACROSS THE CENTRAL GULF AND A 1018 MB SURFACE HIGH
NEAR 26N84W. STABLE ATMOSPHERIC CONDITIONS AND SUBSIDENCE
ASSOCIATED WITH THE SURFACE HIGH AND SURFACE RIDGE ARE RESULTING
IN GENERALLY FAIR WEATHER ACROSS THE GULF. HOWEVER...ACROSS THE
N CENTRAL GULF...UPPER LEVEL MOISTURE IS INTERACTING WITH
ATMOSPHERIC LIFT ASSOCIATED WITH A WEAK SHORTWAVE TROUGH TO
RESULT IN SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS N OF 27N
BETWEEN 86W-95W. ANTICYCLONIC FLOW AROUND THE SURFACE RIDGE IS
SUPPORTING A BROAD SWATH OF E TO SE WINDS OF 10-15 KT ACROSS A
LARGE PART OF S GULF. A WEAK FRONT IS EXPECTED TO PUSH INTO THE
FAR NE GULF DURING THE WEEKEND...BEFORE BECOMING DIFFUSE ON
MONDAY. THE FRONT IS FORECAST TO BE PRECEDED BY A BRIEF PERIOD
OF INCREASING SW WINDS.

CARIBBEAN SEA...
FRESH TO STRONG TRADE WINDS ARE OCCURRING BETWEEN THE
SUBTROPICAL RIDGE OVER THE CENTRAL ATLC AND A BROAD TROUGH OVER
NORTHERN SOUTH AMERICA...WITH THE STRONGEST FLOW NEAR THE COAST
OF COLOMBIA. RECENT SCATTEROMETER DATA INDICATE THAT A LARGE
AREA OF NE TO E WINDS OF 20 TO 30 KT IS PRESENT ACROSS THE S
CARIBBEAN. THESE TRADE WINDS ARE FORECAST TO REMAIN FRESH TO
STRONG INTO THIS WEEKEND AS THE SUBTROPICAL RIDGE REMAINS IN
PLACE. COMPUTER MODEL GUIDANCE INDICATES THAT STRONGER WINDS TO
GALE FORCE ARE OCCURRING NEAR THE COAST OF COLOMBIA...WHERE
WINDS ARE BEING ENHANCED DUE TO LOCAL TOPOGRAPHICAL VARIATIONS
NEAR THE COAST OF COLOMBIA. GALE CONDITIONS ARE FORECAST TO
CONTINUE THROUGH THIS AFTERNOON NEAR THE COAST OF COLOMBIA.
ACROSS MUCH OF THE CENTRAL AND E CARIBBEAN...DEEP LAYER DRY AIR
AND STABLE ATMOSPHERIC CONDITIONS ARE RESULTING IN GENERALLY
FAIR WEATHER.

ATLANTIC OCEAN...
DEEP LAYER MOISTURE IS COMBINING WITH UPPER LEVEL DIFFLUENCE IN
NORTHWESTERLY FLOW ALOFT TO RESULT IN SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS N OF 28N BETWEEN 56W-65W. SUBSIDENCE AND
GENERALLY FAIR WEATHER ARE PRESENT ACROSS MUCH OF THE CENTRAL
AND E ATLC AROUND A BROAD SURFACE RIDGE ASSOCIATED WITH A 1036
MB HIGH NEAR 40N24W. ACROSS THE TROPICAL N ATLC...A SURFACE
TROUGH IS EMBEDDED WITHIN THE ITCZ...AND THIS SURFACE TROUGH
EXTENDS FROM 15N24W TO 11N25W TO 8N24W. RECENT SATELLITE IMAGERY
INDICATES A DISTINCT AREA LOW TO MIDDLE LEVEL CYCLONIC
CIRCULATION IN THE VICINITY OF THIS SURFACE TROUGH. UPPER AIR
DATA OVER BAMAKO IN MALI SUGGEST THAT THIS FEATURE LIKELY MOVED
ACROSS BAMAKO AROUND 15/1200 UTC. SATELLITE IMAGERY DURING THE
LAST TWO DAYS SUGGEST THAT THIS FEATURE COULD BE A TROPICAL
WAVE. ADDITIONAL DATA...INCLUDING UPPER AIR DATA OVER SAL IN THE
CAPE VERDE ISLANDS AND SCATTEROMETER DATA...WILL BE REVIEWED
BEFORE THIS TROUGH IS ANALYZED AS A TROPICAL WAVE. AN UPPER
LEVEL RIDGE EXTENDS FROM 18N26W TO AN UPPER LEVEL HIGH NEAR
16N47W TO 12N60W. UPPER LEVEL DIVERGENCE ASSOCIATED WITH THE
UPPER LEVEL HIGH AND THE UPPER LEVEL RIDGE IS SUPPORTING THE
CONVECTION NEAR THE ITCZ AND NEAR THE TROPICAL WAVE ALONG 33W S
OF 18N.

$$
COHEN




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