[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 212356
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SUN JUN 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...

A TIGHT PRESSURE GRADIENT BETWEEN HIGH PRESSURE ACROSS THE
WESTERN ATLC AND THE GULF OF MEXICO...AND A 1007 MB LOW OVER
NORTHERN COLOMBIA IS SUPPORTING NEAR GALE FORCE WINDS OVER A PORTION
OF THE SOUTH-CENTRAL CARIBBEAN TODAY. THE GRADIENT WILL TIGHTEN
FURTHER TONIGHT...WHICH WILL RESULT IN GALE FORCE WINDS STARTING
10 TO 15 FT ARE EXPECTED. THESE GALE FORCE WINDS ARE FORECAST TO
DIMINISH TOMORROW AHEAD OF A TROPICAL WAVE THAT WILL MOVE ACROSS
THE CENTRAL CARIBBEAN TUE AND WED. PLEASE REFER TO THE HIGH SEAS
FORECAST... MIAHSFAT2/FZNT02 KNHC...AND THE OFFSHORE
FORECAST...MIAOFFNT3/ FZNT23 KNHC...FOR MORE DETAILS.

...TROPICAL WAVES...

A TROPICAL WAVE IS APPROACHING THE CAPE VERDE ISLANDS OVER THE
EASTERN ATLC WITH AXIS ALONG ROUGHLY 21N FROM 07N TO
16N...MOVING W AT AROUND 15 TO 20 KT. SSMI TPW IMAGERY INDICATES
THIS WAVE REMAINS EMBEDDED IN A MODERATE MOIST ENVIRONMENT S OF
15N WITH METEOSAT IMAGERY INDICATING SAHARAN DUST AND DRY AIR N
OF 15N.

A TROPICAL WAVE IS OVER THE CENTRAL TROPICAL ATLC WITH AXIS
ALONG 42W/43W FROM 05N TO 13N...MOVING W AT 20 KT OVER THE PAST
24 HOURS. AN ASCAT SATELLITE PASS FROM AROUND 1830 UTC INDICATED
TRADE WINDS AROUND 20 KT FROM 12N TO 15N BETWEEN 45W AND 50W
BETWEEN THE WAVE AND RIDGING NW OF THE WAVE. SSMI TPW IMAGERY
SHOWS THE WAVE IS EMBEDDED IN A MODERATE MOIST ENVIRONMENT S OF
12N...EXCEPT IN THE NORTHERN REGION WHERE METEOSAT SATELLITE
IMAGERY INDICATES SAHARAN DRY AIR AND DUST. NO DEEP CONVECTION
IS NOTED WITH THE WAVE AT THIS TIME.

A TROPICAL WAVE IS IN THE WESTERN TROPICAL ATLC APPROACHING THE
WINDWARD ISLANDS. THIS WAVE HAS BEEN ACCOMPANIED BY A RELATIVELY
HIGH AMOUNT OF LOWER LEVEL MOISTURE AND IS CURRENTLY INTERACTING
WITH AN UPPER LOW CENTERED NORTH OF THE VIRGIN ISLANDS TO
PRODUCE WIDESPREAD SHOWERS AND THUNDERSTORMS MAINLY SOUTH OF 15N
THROUGHOUT THE WINDWARD ISLANDS. A REGIONAL RADAR MOSAIC IS
SHOWING THE MAIN AREA OF CONVECTION OVER BARBADOS...WHERE AN
OBSERVATION AT 19 UTC INDICATED GUSTS TO 34 KT. THE STRONG
DOWNDRAFTS MAY BE DUE IN PART TO A DRIER PATTERN IN THE MID
LEVELS OF THE ATMOSPHERE RELATED TO THE SAHARAN AIR LAYER. THE
WAVE WILL PASS THE WINDWARD ISLANDS THROUGH OVERNIGHT...BRINGING
CONTINUED SHOWERS AND THUNDERSTORMS WITH OCCASIONALLY HEAVY
RAINFALL AND GUSTY WINDS TO THE ISLANDS THROUGH MONDAY. A FEW
SHOWERS AND THUNDERSTORMS WILL ALSO IMPACT THE LEEWARD ISLANDS
AS THE TROPICAL WAVE AND UPPER LOW SHIFT W OF THE AREA.

A TROPICAL WAVE IS IN THE FAR SW CARIBBEAN BASIN IS STARTING TO
SLOWLY MAKE LANDFALL INTO THE COASTS OF NICARAGUA AND COSTA RICA.
SSMI TPW IMAGERY INDICATES THAT THERE IS ABUNDANT MOISTURE S OF
12N ALONG THE WAVE...WITH DRY AIR N OF 12N. A FEW SHOWERS AND
THUNDERSTORMS ARE NOTED ALONG THE COAST FROM WESTERN PANAMA TO
CENTRAL COSTA RICA DUE TO TRADE WIND CONVERGENCE AND SEA BREEZE
EFFECTS.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS ACROSS AFRICA TO OVER SENEGAL NEAR
14N17W...RESUMING W OF A TROPICAL WAVE NEAR 08N23W AND
CONTINUING TO 05N35W. THE ITCZ BEGINS NEAR 05N35W AND CONTINUES
TO E OF A TROPICAL WAVE NEAR 06N42W. BESIDES THE CONVECTION
ASSOCIATED WITH THE TROPICAL WAVES...ONLY A FEW MODEST SHOWERS
ARE NOTED WITHIN 120 NM N OF THE MONSOON TROUGH AXIS BETWEEN 25W
AND 30W.

...DISCUSSION...

THE GULF OF MEXICO...

AN UPPER LOW REMAINS ANCHORED OVER THE YUCATAN PENINSULA.
SUBSIDENCE ON THE WESTERN SIDE OF THIS FEATURE IS KEEPING THE
WESTERN GULF MOSTLY CLOUD FREE. A FEW SHOWERS AND THUNDERSTORMS
ARE NOTED OVER THE SE GULF UNDER DIVERGENCE ALOFT ASSOCIATED
WITH THE UPPER LOW. A 1020 MB SURFACE HIGH REMAINS CENTERED OVER
THE NORTHEAST GULF NEAR 27N87W. THIS IS MAINTAINING GENERALLY
LIGHT TO GENTLE BREEZES OVER THE EASTERN GULF. RECENT
OBSERVATIONS ALONG THE COAST OF TEXAS ALONG WITH A 16 UTC ASCAT
SATELLITE PASS INDICATED MODERATE TO LOCALLY FRESH RETURN FLOW
HAS SET UP OVER THE NW GULF BETWEEN THE HIGH PRES AND LOW PRES
OVER N CENTRAL MEXICO. FARTHER SOUTH...A TROUGH HAS FORMED OVER
THE YUCATAN PENINSULA DUE TO STRONG ADIABATIC WARMING. THE
TROUGH WILL MIGRATE WEST TONIGHT IN PHASE WITH THE NORTHERN
EXTENT OF A TROPICAL WAVE MOVING ACROSS CENTRAL AMERICA TO
MAINTAIN MODERATE TO FRESH WINDS OVER THE SW GULF TONIGHT. SEAS
ARE RANGING FROM 1 TO 3 FT OVER THE NE GULF...2 TO 4 FT OVER THE
NW AND SE GULF...3 TO 5 FT IN THE SW GULF WITH LITTLE CHANGE
EXPECTED THROUGH EARLY NEXT WEEK.

THE CARIBBEAN SEA...

STRONG RIDGING EXTENDS FROM THE WESTERN ATLC TO THE CENTRAL
CARIBBEAN IN THE WAKE OF A TROPICAL WAVE MOVING INTO CENTRAL
AMERICA. A TIGHT GRADIENT BETWEEN THE RIDGE AND LOW PRES OVER
COLOMBIA IS RESULTING IN NEAR GALE FORCE WINDS ACROSS MUCH OF
THE CENTRAL CARIBBEAN...PULSING TO GALE FORCE TONIGHT. ANOTHER
TROPICAL WAVE APPROACHING THE WINDWARD ISLANDS WILL MOVE INTO
THE EASTERN CARIBBEAN BY EARLY MON...AND INTO THE CENTRAL
CARIBBEAN BY LATE TUE. THIS TROPICAL WAVE IS INTERACTING WITH A
BROAD UPPER LOW CURRENTLY CENTERED JUST NORTH OF THE VIRGIN
ISLANDS...AND WILL BRING INCREASED SHOWERS AND THUNDERSTORMS TO
MUCH OF THE EASTERN AND CENTRAL CARIBBEAN THROUGH EARLY NEXT
WEEK.

...HISPANIOLA...

A FEW THUNDERSTORMS FORMED THIS AFTERNOON OVER THE NORTHERN AND
CENTRAL MOUNTAIN RANGES OF THE DOMINICAN REPUBLIC BUT WERE
SHEARED BY STRONG NORTHERLY FLOW ON THE WEST SIDE OF AN UPPER
LOW CURRENTLY CENTERED NORTH OF THE VIRGIN ISLANDS. THE UPPER
LOW ALONG WITH A TRAILING TROPICAL WAVE WILL MOVE WEST AND
APPROACH EASTERN HISPANIOLA BY EARLY TUE. THE TROPICAL WAVE WILL
MOVE SLOWLY THROUGH THE CENTRAL CARIBBEAN THROUGH MID WEEK...AND
THE UPPER LOW WILL GENERALLY STALL OVER HISPANIOLA. THIS WILL
INCREASE CHANCES FOR SHOWERS AND THUNDERSTORMS MAINLY DURING
AFTERNOON HOURS OVER THE ISLAND EARLY TO MID WEEK.

THE ATLANTIC OCEAN...

S OF 31N W OF 60W...A FEW SHOWERS AND THUNDERSTORMS ARE NOTED
ACROSS THE NORTHERN BAHAMAS AND WITHIN 300 NM NE OF THE NORTHERN
BAHAMAS...RELATED TO DIVERGENCE ALOFT BETWEEN AN UPPER RIDGE
CENTERED NEAR 29N72W AND AN UPPER LOW CENTERED JUST NORTH OF THE
VIRGIN ISLANDS. THE SUBTROPICAL RIDGE AXIS EXTENDS EAST TO WEST
ALONG ROUGHLY 29N...MAINTAINING LIGHT TO GENTLE BREEZES N OF 22N
AND MODERATE TO FRESH WINDS SOUTH OF 22N. LOOKING AHEAD...THE
NORTHERN PORTION OF A TROPICAL WAVE WILL TRAIL THE UPPER LOW AS
IT SHIFT WESTWARD THROUGH MID WEEK...BRINGING AN SLIGHT INCREASE
IN EAST WINDS PARTICULARLY N OF HISPANIOLA MON AND TUE ALONG
WITH INCREASED SHOWERS AND THUNDERSTORMS S OF 22N.

CENTRAL AND EASTERN ATLC...BROAD SURFACE RIDGING COVERS THE
CENTRAL ATLC BEING ANCHORED BY A 1027 MB HIGH NEAR
28N41W...MAINTAINING GENTLE TO MODERATE BREEZES N OF 22N AND
MODERATE TO FRESH TRADES S OF 22N...MAINLY NEAR TROPICAL WAVES.
METEOSAT SATELLITE IMAGERY INDICATES SAHARAN DRY AIR AND DUST
COVERING MOST OF THE TROPICS S OF 20N...MAINLY E OF 30W WHERE A
NEW PLUME IS EMERGING OFF THE COAST OF NW AFRICA.

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

$$
CHRISTENSEN
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