[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 212342
TWDAT

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

...SPECIAL FEATURES...

HURRICANE DANNY CENTERED NEAR 14.5N 49.1W AT 21/2100 UTC OR 860
NM E OF THE LEEWARD ISLANDS MOVING WNW AT 9 KT. ESTIMATED
MINIMUM CENTRAL PRESSURE IS 974 MB. MAXIMUM SUSTAINED WIND
SPEED IS 100 KT WITH GUSTS TO 120 KT. SCATTERED MODERATE TO
STRONG CONVECTION IS WITHIN 75 NM OF THE CENTER WITH SCATTERED
MODERATE CONVECTION ELSEWHERE WITHIN 180 NM IN THE N QUADRANT
OF THE CENTER. DANNY HAS LIKELY REACHED ITS PEAK INTENSITY AND
THE OFFICIAL FORECAST HAS DANNY WEAKENING THROUGH THE FORECAST
PERIOD...WITH A TROPICAL STORM STATUS EXPECTED BY 48 HOURS. SEE
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS.

...TROPICAL WAVES...

A TROPICAL WAVE HAS EMERGED FROM THE W COAST OF AFRICA WITH AN
AXIS EXTENDING FROM 18N21W TO 08N20W MOVING W AT AROUND 10 KT.
SAHARAN DRY AIR IS LOCATED MAINLY N OF THE WAVE AXIS WHICH HAS
ALLOWED FOR SOME ISOLATED TO WIDELY SCATTERED MODERATE
CONVECTION FROM 12N-16N BETWEEN 17W-21W...AND ALSO FROM 06N-10W
BETWEEN 16W-26W. THE WAVE COINCIDES WITH AN 850 MB VORTICITY
MAXIMUM FROM 12N-15N BETWEEN 17W-23W WHILE THE 700 MB TROUGH
AXIS IS NOTED JUST OUT AHEAD OF THE WAVE.

A TROPICAL WAVE AXIS EXTENDS FROM 21N33W TO 05N33W AND IS MOVING
W AROUND 10-15 KT. THIS WAVE IS EMBEDDED IN SAHARAN DRY AIR AND
STABLE CONDITIONS WHICH IS INHIBITING CONVECTION WITH NOT EVEN
ISOLATED SHOWERS EVIDENT NEAR THE WAVE AXIS. WEAK VORTICITY IS
NOTED FROM 13N-21W ALONG THE WAVE AXIS AND THE 700 MB TROUGH
AXIS IS NOTED JUST OUT AHEAD OF THE NORTHERN PORTION OF THE WAVE.

A TROPICAL WAVE IS MOVING FROM THE CENTRAL TO THE W CARIBBEAN
WITH AN AXIS EXTENDING FROM CENTRAL JAMAICA NEAR 18N77W TO JUST
NW OF THE COAST OF COLOMBIA NEAR 10N77W MOVING W AT AROUND 15-20
KT. THE WAVE IS ENCOUNTERING DRY AND STABLE AIR ALOFT WITH NO
DIRECTLY ASSOCIATED CONVECTION PRESENT. WEAK 850 MB VORTICITY
MAXIMUM IS NOTED ALONG THE WAVE AXIS WHILE A 700 MB TROUGH IS
EVIDENT JUST W OF THE TROPICAL WAVE AXIS.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH AXIS EXTENDS FROM THE W COAST OF AFRICA NEAR
14N17W TO 07N27W TO 09N41W. NO WELL DEFINED ITCZ AXIS IS NOTED
AT THIS TIME MAINLY DUE TO THE PRESENCE OF HURRICANE DANNY.
ISOLATED TO SCATTERED MODERATE CONVECTION IS FROM 05N-07N
BETWEEN 26W-31W.

...DISCUSSION...

GULF OF MEXICO...

AN UPPER LEVEL RIDGE EXTENDS ACROSS THE NORTHERN PART OF THE
GULF FROM 29N83W TO THE SW-W TO NEAR 25N96W. AN UPPER LEVEL
CYCLONE IS PRESENT OVER THE YUCATAN PENINSULA NEAR 19N90W.
ISOLATED CONVECTION IS OCCURRING AROUND THE PERIPHERY OF BOTH
UPPER LEVEL FEATURES WITH NO SIGNIFICANTLY ORGANIZED CONVECTION.
LIGHT AND VARIABLE ANTICYCLONIC WINDS AND 1-3 FT SEAS WILL
PERSIST ACROSS THE NE HALF OF THE GULF...WITH MODERATE TO
LOCALLY FRESH SE RETURN FLOW AND 3-6 FT SEAS ACROSS THE SW HALF
OF THE GULF. THE STRONGEST WINDS ARE EXPECTED NW-N OF THE
YUCATAN PENINSULA DURING THE EVENING AND OVERNIGHT HOURS AS
DIURNAL TROUGHING DEVELOPS OVER THE PENINSULA EACH AFTERNOON
BEFORE MOVING TO THE W OFFSHORE INTO THE SW GULF WHERE IT WILL
DISSIPATE BY SUNRISE EACH DAY. THESE CONDITIONS ARE FORECAST TO
PERSIST THROUGH THE NEXT 48 HOURS.

CARIBBEAN SEA...

AN UPPER LEVEL CYCLONE IS LOCATED OVER THE YUCATAN PENINSULA
NEAR 19N90W WHILE AN UPPER LEVEL ANTICYCLONE IS LOCATED OVER THE
SW CARIBBEAN NEAR 11N78W. W OF 72W...ONLY ISOLATED CONVECTIVE
ACTIVITY IS OCCURRING AROUND THE PERIPHERY OF BOTH OF THESE
FEATURES. E OF 72W...UPPER LEVEL TROUGHING IS SHIFTING S
SLIGHTLY INTO THE NE PART OF THE BASIN EXTENDING FROM 18N63W TO
ACROSS HISPANIOLA. MAINLY DRY AND STABLE AIR IS EVIDENT ON WATER
VAPOR SATELLITE IMAGERY. MAINLY MODERATE TO LOCALLY FRESH TRADES
AND 3-6 FT SEAS WILL PREVAIL ACROSS THE BASIN THROUGH THE
WEEKEND...EXCEPT IN THE S CENTRAL CARIBBEAN WHERE THE PRES
GRADIENT WILL BE TIGHT ENOUGH TO SUPPORT OCCASIONAL WINDS TO 20-
25 KT WHICH WILL BUILD SEAS TO 7-9 FT.

...HISPANIOLA...

SHALLOW LOW TO MID LEVEL MOISTURE COMBINED WITH DAYTIME HEATING
AND OROGRAPHIC LIFTING HAS RESULTED IN ISOLATED SHOWERS AND
TSTMS ACROSS THE ISLAND DURING THE AFTERNOON INTO THE EARLY
EVENING HOURS. THIS CONVECTIVE ACTIVITY SHOULD DIMINISH SHORTLY
AFTER SUNSET WITH THE LOSS OF DAYTIME HEATING. SIMILAR
DEVELOPMENT OF SHOWERS AND TSTMS IS POSSIBLE THROUGH THE
WEEKEND WITH LITTLE CHANGE IN ATMOSPHERIC CONDITIONS ANTICIPATED.

ATLANTIC OCEAN...

AN UPPER LEVEL ANTICYCLONE IS LOCATED JUST E OF NORTHERN FLORIDA
NEAR 29N80W. AN UPPER LEVEL CYCLONE IS JUST N OF THE DISCUSSION
WATERS NEAR 34N66W WITH A TRAILING UPPER TROUGH EXTENDING S-SW
THROUGH 30N64W TO 26N76W. THE UPPER CYCLONE AND TROUGH ARE
SUPPORTING A 1012 MB LOW NEAR 29N63W WITH A SURFACE TROUGH
EXTENDING FROM 32N62W TO THE LOW TO THE SW-W TO 27N73W.
SCATTERED SHOWERS AND TSTMS ARE OCCURRING WITHIN 180-210 NM
AHEAD OF THE SURFACE TROUGHING. THE LOW IS FORECAST TO MOVE TO
THE NW REACHING 33N67W IN 24 HOURS. LIGHT AND VARIABLE WINDS
WILL PERSIST ACROSS THE ENTIRE SW N ATLC OFFSHORE WATERS BASIN
THROUGH THE NEXT 48 HOURS. SEAS OF 3 FT OR LESS ARE EXPECTED W
OF 70W...WITH 3-5 FT SEAS E OF 70W. A 1017 MB SURFACE LOW IS
LOCATED OVER THE CENTRAL ATLC NEAR 29N46W WITH A WEAK SURFACE
TROUGH ACCOMPANYING IT. THE LOW IS FORECAST TO DISSIPATE BY 24
HOURS AS RIDGING NE OF THE AREA BUILDS SOUTHWESTWARD.

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

$$
LEWITSKY
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