[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 212347
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT TUE JUL 21 2015

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.

...TROPICAL WAVES...
TROPICAL WAVE EXTENDS FROM 09N26W TO 17N24W MOVING W AT 15 KT.
THE WAVE COINCIDES WITH A VERY BROAD AND SUBTLE 700 MB TROUGH
NOTED IN GLOBAL MODEL GUIDANCE BETWEEN 21W-27W. A NARROW AND
WEAK AREA OF 850 MB RELATIVE VORTICITY ALSO EXTENDS ACROSS THE
WAVE AXIS FROM 14N22W TO 08N35W INDICATING THE STRETCHED OUT
NATURE OF THE ENERGY ASSOCIATED WITH THE WAVE. NO SIGNIFICANT
DEEP CONVECTION IS OCCURRING WITH THE WAVE AT THIS TIME DUE TO
SAHARAN DUST COVERING MUCH OF THE EASTERN TROPICAL ATLC.

TROPICAL WAVE EXTENDS FROM 08N62W TO 18N59W MOVING W AT 20 KT.
THE WAVE COINCIDES WITH 700 MB TROUGHING ALOFT BETWEEN 57W-64W
ON THE SOUTHWESTERN PERIPHERY OF A MID-LEVEL RIDGE CENTERED OVER
THE CENTRAL ATLC NEAR 23N52W. SCATTERED MODERATE AND ISOLATED
STRONG CONVECTION IS OCCURRING FROM 08N-11N BETWEEN 57W-64W...
WITH SCATTERED MODERATE CONVECTION FROM 11N-15N BETWEEN 58W-64W.

TROPICAL WAVE EXTENDS FROM OVER NW VENEZUELA NEAR 07N69W TO THE
SOUTH COAST OF THE DOMINICAN REPUBLIC NEAR 18N68W MOVING W AT 15-
20 KT. THE WAVE REMAINS EMBEDDED WITHIN A NARROW MAXIMUM OF
TOTAL PRECIPITABLE WATER BETWEEN 65W-72W THAT STRETCHES NORTH-
NORTHEASTWARD FROM THE WAVE AXIS...FOCUSED ALONG A SURFACE
TROUGH EXTENDING FROM 19N68W TO 25N61W. THE MOISTURE THEN
EXTENDS INTO THE INFLUENCE OF AN UPPER LEVEL TROUGH AXIS
EXTENDING OVER THE CENTRAL ATLC. ISOLATED TO SCATTERED MODERATE
CONVECTION IS FROM 11N-17N BETWEEN 66W-72W...WITH MORE
CONCENTRATED SCATTERED MODERATE TO STRONG CONVECTION OVER
NORTHERN VENEZUELA FROM 07N-11N BETWEEN 64W-72W.

TROPICAL WAVE EXTENDS FROM THE NORTHEAST PACIFIC OCEAN AND THE
GULF OF PANAMA NEAR 06N80W TO 17N77W MOVING W AT 20-25 KT. THE
WAVE COINCIDES WITH VERY BROAD 700 MB TROUGHING BETWEEN 76W-82W
AND IS LARGELY INFLUENCED ALOFT BY AN UPPER LEVEL RIDGE CENTERED
OVER THE SW CARIBBEAN NEAR 14N80W. ISOLATED MODERATE CONVECTION
IS FROM 08N-11N BETWEEN 78W-82W.

...ITCZ/MONSOON TROUGH...
THE MONSOON TROUGH AXIS EXTENDS FROM THE AFRICAN COAST NEAR
14N17W TO 11N20W TO 08N30W. THE INTERTROPICAL CONVERGENCE ZONE
AXIS EXTENDS FROM 08N30W TO 05N44W TO 10N58W. ISOLATED TO WIDELY
SCATTERED MODERATE CONVECTION IS FROM 09N-11N BETWEEN 19W-22W...
AND FOR A GREAT DISTANCE WITHIN 60 NM EITHER SIDE OF THE AXIS
BETWEEN 31W-57W.

...DISCUSSION...

GULF OF MEXICO...
NORTHEAST TO EASTERLY FLOW ALOFT PREVAILS OVER MUCH OF THE GULF
THIS EVENING BETWEEN A MIDDLE TO UPPER LEVEL ANTICYCLONIC
CIRCULATION CENTERED OVER SOUTH CENTRAL TEXAS NEAR 29N101W AND
AN UPPER LEVEL LOW CENTERED OVER THE NORTHERN YUCATAN PENINSULA
NEAR 21N88W. WHILE A MAJORITY OF THE BASIN IS UNDER THIS
RELATIVELY STABLE FLOW...AT THE SURFACE...WEAK AND ILL-DEFINED
TROUGHING AND LOW-LEVEL MOISTURE CONVERGENCE IS PRESENT ACROSS
THE NE GULF STEMMING FROM A WEAK STREAM OF 500 MB RELATIVE
VORTICITY EXTENDING FROM OVER THE FLORIDA BIG BEND REGION SW TO
OVER THE NW GULF NEAR 27N93W. THIS MID-LEVEL VORTICITY IS
PROVIDING FOCUS FOR SCATTERED SHOWERS AND ISOLATED TSTMS
OCCURRING FROM 26N-30N BETWEEN 83W-92W. OTHERWISE...A SURFACE
RIDGE AXIS EXTENDS FROM 1018 MB HIGH PRESSURE IN THE SE GULF
NEAR 24N84W TO THE NW ALONG THE TEXAS COAST NEAR 29N96W. GENTLE
TO OCCASIONAL MODERATE BREEZE ANTICYCLONIC FLOW IS FORECAST
ACROSS THE BASIN THROUGH LATE THURSDAY...EXCEPT NW OF THE
YUCATAN PENINSULA WHERE WINDS WILL INCREASE TO 20 KT DURING THE
OVERNIGHT HOURS DUE TO DIURNAL TROUGHING WHICH WILL DEVELOP OVER
THE PENINSULA EACH LATE AFTERNOON PUSHING W INTO THE SW GULF
EACH EVENING.

CARIBBEAN SEA...
THE MAIN IMPACT FOR THE CARIBBEAN BASIN THIS EVENING IS THREE
TROPICAL WAVES WHICH ARE MOVING WESTWARD. WHILE THOSE ARE
DETAILED ABOVE...WATER VAPOR IMAGERY INDICATES THAT MOST OF THE
MOISTURE IS FOUND E OF 72W AS DRY AIR ALOFT REMAINS IN PLACE
OVER THE WESTERN CARIBBEAN IN ASSOCIATION WITH AN UPPER LEVEL
RIDGE ANCHORED NEAR 13N80W. FARTHER EAST...MOISTURE AND
CLOUDINESS INCREASES WITH LOW-LEVEL MOISTURE CONVERGENCE
OCCURRING ALONG A LINE EXTENDING FROM 12N61W TO 14N70W N OF THE
A-B-C ISLANDS. WIDELY SCATTERED SHOWERS AND TSTMS ARE OCCURRING
S OF THIS LINE AND ALSO NEAR THE EASTERN TWO TROPICAL WAVE AXIS
AS IS DESCRIBED IN DETAILED ABOVE. MODERATE TO FRESH BREEZE
TRADES ARE EXPECTED TO PERSIST THROUGH LATE THURSDAY EXCEPT IN
THE S CENTRAL PORTION WHERE THE PRESSURE GRADIENT WILL BE THE
MOST TIGHT BETWEEN CENTRAL ATLC HIGH PRESSURE N-NE OF THE AREA
AND LOW PRESSURE OVER NORTHERN COLOMBIA...RESULTING IN FRESH TO
STRONG TRADES. WINDS ARE ALSO FORECAST TO PULSE TO FRESH TO
STRONG LEVELS IN THE GULF OF HONDURAS DURING THE OVERNIGHT HOURS
DUE TO A LOCALLY AND DIURNALLY DRIVEN STRENGTHENING PRESSURE
GRADIENT.

...HISPANIOLA...
CURRENTLY...THE NORTHERN PORTION OF A TROPICAL WAVE IS HELPING
TO IGNITE SCATTERED SHOWERS AND TSTMS ACROSS THE ISLAND E OF 70W
WITH ISOLATED ACTIVITY ALSO NOTED TO THE W ACROSS NORTHERN
HAITI. THE PASSAGE OF THE TROPICAL WAVE DURING THE NEXT 24 HOURS
OR SO WILL RESULT IN A CONTINUED HIGHER PROBABILITY OF SCATTERED
SHOWERS AND TSTMS...ESPECIALLY DURING THE AFTERNOON AND EVENING
HOURS WITH THE ADDITION OF DAYTIME HEATING.

ATLANTIC OCEAN...
NORTH-NORTHEASTERLY FLOW ALOFT PREVAILS OVER MUCH OF THE SW
NORTH ATLC BETWEEN AN UPPER LEVEL ANTICYCLONE CENTERED NEAR
30N79W AND AN UPPER LEVEL LOW CENTERED NEAR 23N63W. WHILE
OVERALL CONDITIONS REMAIN STABLE ACROSS THE SW NORTH ATLC WITHIN
A SURFACE RIDGE WITH AXIS ALONG 26N/27N...LOW-LEVEL MOISTURE
CONVERGENCE IS MAXIMIZED ALONG A LINE FROM 26N80W TO 31N74W WITH
ISOLATED SHOWERS AND TSTMS OCCURRING N OF THIS LINE. FARTHER
EAST...WITHIN THE INFLUENCE OF THE UPPER LEVEL LOW...A SURFACE
TROUGH...THE NORTHERN PIECE OF ENERGY FRACTURED AWAY FROM A
TROPICAL WAVE IN THE CARIBBEAN SEA ALONG 68W...IS GENERATING
SCATTERED SHOWERS AND ISOLATED TSTMS WITHIN 45 NM EITHER SIDE OF
A LINE FROM 28N54W TO 20N67W. OTHERWISE...A NEARLY STATIONARY
RIDGE ANCHORED BY A 1023 MB HIGH CENTERED NEAR 28N46W INFLUENCES
THE REMAINDER OF THE CENTRAL AND EASTERN ATLC.

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

$$
LEWITSKY
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