[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 202308
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT THU AUG 20 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.

...SPECIAL FEATURES...

HURRICANE DANNY CENTERED NEAR 13.0N 45.7W AT 20/2100 UTC OR 895
NM E OF THE WINDWARD ISLANDS MOVING WNW AT 9 KT. ESTIMATED
MINIMUM CENTRAL PRESSURE IS 990 MB. MAXIMUM SUSTAINED WIND
SPEED IS 70 KT WITH GUSTS TO 85 KT. SCATTERED MODERATE TO STRONG
CONVECTION IS WITHIN 45 NM OF THE CENTER WITH A BANDING FEATURE
OF SCATTERED MODERATE CONVECTION BETWEEN 45 NM AND 105 NM IN THE
NW SEMICIRCLE. THE OFFICIAL FORECAST IS FOR DANNY TO STRENGTHEN
SLIGHTLY DURING THE NEXT 24 HOURS WITH SLIGHT WEAKEN THEN
EXPECTED BETWEEN 24 AND 48 HOURS. SEE LATEST NHC FORECAST/
ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC FOR
MORE DETAILS.

...TROPICAL WAVES...

A TROPICAL WAVE OVER THE EASTERN ATLC HAS AN AXIS THAT EXTENDS
FROM 22N26W TO 06N28W MOVING W AT AROUND 10 KT. TOTAL
PRECIPITABLE WATER SATELLITE IMAGERY SHOWS A POLEWARD SURGE IN
MOISTURE ASSOCIATED WITH THE WAVE. A 700 MB TROUGH IS NOTED FROM
09N-17N AND 850 MB RELATIVE VORTICITY MAXIMUM ALONG THE WAVE
AXIS. SAHARAN DRY AIR SURROUNDS THE WAVE AND ONLY ISOLATED TO
SCATTERED SHOWERS NEAR THE WAVE AXIS.

A TROPICAL WAVE EXTENDS FROM THE EASTERN SHORE OF PUERTO RICO
NEAR THE ANEGADA PASSAGE TO N CENTRAL VENEZUELA NEAR 09N66W
MOVING W AT AROUND 20 KT. TPW SATELLITE IMAGERY INDICATES A
SURGE OF MOISTURE NEAR THE WAVE AXIS AND ACROSS THE LESSER
ANTILLES. A 700 MB TROUGH IS NOTED AHEAD OF THE LOWER LEVEL WAVE
AXIS FROM 12N-18W. LIMITED CONVECTION IS NOTED WITH THE WAVE AS
IT IS UNDER AN AREA OF SUBSIDENCE AND STABLE CONDITIONS...EXCEPT
OVER NORTHERN VENEZUELA WHERE TSTM ACTIVITY IS PRESENT.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH AXIS EXTENDS FROM WESTERN AFRICA NEAR 14N17W
TO 08N87W TO 09N38W. A WEAK ITCZ AXIS EXTENDS FROM NEAR 10N48W
TO 09N59W. SCATTERED MODERATE CONVECTION IS NOTED FROM 07N-15N E
OF 22W...AND FROM 09N-13N BETWEEN 57W-64W.

...DISCUSSION...

GULF OF MEXICO...

A BROAD MID TO UPPER LEVEL ANTICYCLONE IS CENTERED OVER THE NE
GULF NEAR 28N86W EXTENDING A RIDGE AXIS TO THE S-SW THROUGH
24N93W TO 21N94W. AN UPPER TROUGH IS LOCATED TO THE W OVER
CENTRAL TEXAS. CONVECTION PERSISTS AROUND THE PERIPHERY OF THE
RIDGE AND AHEAD OF THE UPPER TROUGH HOWEVER CONDITIONS OVER THE
GULF WATERS ARE MAINLY FAIR WITH A MOSTLY CLEAR SKY. A 1017 MB
SURFACE HIGH IS LOCATED IN THE SE GULF NEAR 26N84W. MAINLY LIGHT
ANTICYCLONIC WINDS WILL PERSIST ACROSS THE NE HALF OF THE GULF
THROUGH THE NEXT 48 HOURS...WITH MODERATE TO LOCALLY FRESH SE
RETURN FLOW ACROSS THE SW HALF OF THE GULF. WINDS WILL INCREASE
TO FRESH TO STRONG NW-N OF THE YUCATAN PENINSULA DURING THE
EVENING AND OVERNIGHT HOURS AS A SURFACE TROUGH DEVELOPS INLAND
AND MOVES W OFFSHORE INTO THE SW GULF EACH NIGHT BEFORE
DISSIPATING.

CARIBBEAN SEA...

A LARGE UPPER LEVEL CYCLONE IS IN THE NW CARIBBEAN NEAR 18N86W.
AN UPPER LEVEL ANTICYCLONE IS CENTERED OVER THE S CENTRAL
CARIBBEAN JUST N OF THE COAST OF COLOMBIA NEAR 13N73W AND
EXTENDS A RIDGE AXIS TO THE NW-N TO EASTERN CUBA. MAINLY DRY AND
STABLE AIR IS PRESENT ACROSS THE BASIN E OF 74W WHILE ISOLATED
SHOWERS AND TSTMS ARE OCCURRING W OF 74W AROUND THE UPPER
CYCLONE. MAINLY MODERATE TO LOCALLY FRESH TRADES WILL PREVAIL
ACROSS THE BASIN THROUGH THE NEXT 48 HOURS...EXCEPT IN THE S
CENTRAL CARIBBEAN WHERE WINDS WILL BE STRONG TO NEAR GALE FORCE
DUE TO A TIGHT PRES GRADIENT BETWEEN CENTRAL ATLC HIGH PRES AND
LOW PRES OVER NORTHERN COLOMBIA. CONDITIONS WILL IMPROVE IN THE
S CENTRAL CARIBBEAN THIS WEEKEND AS THE PRES GRADIENT RELAXES.
WINDS WILL ALSO PULSE TO FRESH TO STRONG LEVELS IN THE GULF OF
HONDURAS EACH EVENING. SEAS WILL BE PRIMARILY 3-6 FT...EXCEPT 7-
11 FT IN THE S CENTRAL CARIBBEAN...SUBSIDING THIS WEEKEND.

...HISPANIOLA...

MARGINAL LOW TO MID LEVEL MOISTURE HAS COMBINED WITH DAYTIME
HEATING AND OROGRAPHIC LIFTING TO GENERATE ISOLATED SHOWERS AND
TSTMS OVER THE ISLAND THIS AFTERNOON HOWEVER THE ACTIVITY SHOULD
DIMINISH SHORTLY AFTER SUNSET. A TROPICAL WAVE WILL THEN
APPROACH THE ISLAND OVERNIGHT MOVING ACROSS ON FRI WHICH WILL
LIKELY ENHANCE THE CHANCE FOR SHOWERS AND TSTMS INTO THE FIRST
PART OF THE WEEKEND.

ATLANTIC OCEAN...

AN UPPER RIDGE AXIS EXTENDS ACROSS THE SW N ATLC OFFSHORE WATERS
FROM S FLORIDA TO THE E-SE ACROSS THE BAHAMAS TO NEAR 25N55W. AN
UPPER CYCLONE IS N OF THE AREA NEAR 35N64W WITH AN UPPER TROUGH
REACHING TO THE SW TO NEAR 29N70W. ISOLATED TO WIDELY SCATTERED
CONVECTION IS FIRING AHEAD OF THE TROUGH. THESE UPPER FEATURES
SUPPORT A 1012 MB SURFACE LOW NEAR 30N68W WITH SURFACE TROUGHING
EXTENDING FROM THE LOW FROM 27N-31N. THIS LOW IS FORECAST TO
MOVE TO E AROUND 10-15 KT DURING THE NEXT 24-48 HOURS. SURFACE
HIGH PRES AT 1017 MB IS LOCATED TO THE SW NEAR 25N72W. FRESH
WINDS AND SEAS OF 5-7 FT ARE FORECAST AHEAD OF THE LOW AND
TROUGH. LIGHT TO MODERATE ANTICYCLONIC FLOW PREVAILS OUTSIDE OF
THE INFLUENCE OF THE MENTIONED SURFACE LOW AND TROUGHING. THE
SURFACE HIGH WILL DISSIPATE AS THE LOW DRAGS THE TRAILING
TROUGHING TO THE S-SW THROUGH THE NEXT 24-48 HOURS.

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

$$
LEWITSKY
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