[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 192346
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT THU JUL 19 2012

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
2245 UTC.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 17N39W TO 9N46W MOVING W NEAR 20 KT. WAVE
WAS ALIGNED WITH A TILT TO BETTER FIT THE SHAPE OF A BROAD SURGE
OF DEEP LAYER MOISTURE THAT TRAILS THE WAVE SEEN IN TOTAL
PRECIPITABLE IMAGERY. DUE TO THE LARGE AREA OF SAHARAN DUST
COVERING THE TROPICAL ATLC...NO DEEP CONVECTION IS ASSOCIATED
WITH THE WAVE EXCEPT FOR A SMALL AREA OF MODERATE CONVECTION
FROM 7N-8N BETWEEN 47W-49W.

TROPICAL WAVE IS MOVING THROUGH THE ERN CARIBBEAN ALONG 20N67W
TO 12N63W. THE WAVE LIES ON THE W SIDE OF A TILTED SURGE OF DEEP
LAYER MOISTURE PRESENT IN TOTAL PRECIPITABLE WATER
IMAGERY...WHICH EXPLAINS THE TILT OF THE WAVE. ISOLATED MODERATE
CONVECTION IS WITHIN 200 NM E AND 150 NM W OF THE AXIS. A LARGE
AREA OF SAHARAN DUST IS IMMEDIATELY E OF THE WAVE. THIS WAVE IS
APPROACHING AN UPPER LEVEL LOW NEAR ERN CUBA. SHOWER ACTIVITY
SHOULD INCREASE NEAR THE WAVE AS IT APPROACHES THE ERN AND
DIFFLUENT SIDE OF THE UPPER LOW.

TROPICAL WAVE IS MOVING THROUGH THE BAY OF CAMPECHE ALONG 23N94W
TO 17N93W MOVING W NEAR 15-20 KT. THE WAVE IS ON THE E SIDE OF
AN AREA OF ENHANCED DEEP LAYER MOISTURE THAT COVERS THE FAR WRN
GULF OF MEXICO. HOWEVER...IT LIES ON THE WRN SIDE OF AN UPPER
LEVEL LOW WHICH IS DRAWING DRY AIR ALOFT OVER THE WAVE. THIS IS
PREVENTING CONVECTION NEAR THE AXIS. THERE ARE AREAS REMOVED
FROM THE WAVE TO EITHER SIDE...BUT ARE LIKELY TIED TO THE UPPER
LOW AND A SECOND UPPER LOW OVER N CENTRAL MEXICO.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS ACROSS W AFRICA TO THE COAST OF
GUINEA-BISSAU AT 13N16W CONTINUING ALONG 14N30W TO 9N49W. THE
ITCZ BEGINS AT 9N49W CONTINUING TO 9N61W. NO DEEP CONVECTION IS
ALONG THE AXIS...BUT A LARGE BURST OF CONVECTION IS NEARING THE
AFRICAN COASTLINE.

...DISCUSSION...

GULF OF MEXICO...
A PAIR OF UPPER LEVEL LOWS CONTINUE TO IMPACT THE GULF OF MEXICO
TONIGHT SUPPORTING SHOWERS/THUNDERSTORMS IN THE NE AND SW
CORNER. THE FIRST UPPER LOW IS CENTERED OVER ERN GEORGIA NEAR
32N82W SUPPORTING WIDESPREAD SHOWERS/THUNDERSTORMS N OF 27N
BETWEEN 86W-92W ACROSS MUCH OF MISSISSIPPI AND ERN LOUISIANA.
THE SECOND UPPER LOW IS CENTERED OVER THE ERN BAY OF CAMPECHE
NEAR 20N91W. IT IS SUPPORTING SCATTERED SHOWERS AND
THUNDERSTORMS ACROSS THE YUCATAN PENINSULA. A TROPICAL WAVE IS
IMMEDIATELY W OF THE UPPER LOW PLACING IT ON THE CONFLUENT SIDE
OF THE UPPER LOW...WHICH IS LIMITING CONVECTION NEAR THE WAVE AS
DRY AIR WRAPS AROUND IT. HOWEVER...SCATTERED
SHOWERS/THUNDERSTORMS ARE ACROSS THE FAR WRN BAY OF CAMPECHE DUE
TO A THIRD UPPER LEVEL LOW/TROUGH THAT IS CENTERED OVER N
CENTRAL MEXICO WITH TROUGH AXIS EXTENDING DOWN THE CENTER OF THE
COUNTRY PLACING THE EXTREME WRN GULF UNDER THE DIFFLUENT SIDE OF
THE LOW/TROUGH. THE REMAINDER OF THE GULF IS COVERED BY AN UPPER
LEVEL RIDGE ACROSS THE NRN PORTION OF THE BASIN SUPPORTING A
WEAK SURFACE RIDGE AROUND A 1020 MB HIGH OVER SW ALABAMA.
BESIDES NEAR THE UPPER LOWS...DRY AIR COVERS THE BASIN KEEPING
THE REMAINDER OF IT UNDER CLEAR SKIES AND FAIR CONDITIONS. WEAK
SURFACE RIDGING WILL FORM REMAIN ACROSS THE BASIN AS THE UPPER
LEVEL LOWS WEAKEN. MOISTURE MAY REMAIN OVER SOME PORTIONS OF THE
NE GULF WHERE THE HIGHEST CHANCE OF SHOWERS/THUNDERSTORMS WILL
BE.

CARIBBEAN SEA...
THE UPPER LEVEL LOW OVER THE ERN BAY OF CAMPECHE IS SUPPORTING
SCATTERED SHOWERS/THUNDERSTORMS ACROSS THE YUCATAN PENINSULA AND
WATERS TO THE E TO 85W. CLUSTERS OF STRONG SHOWERS/THUNDERSTORMS
ARE ALSO ACROSS SRN CUBA AND ADJACENT WATERS AS WELL AS JAMAICA.
THESE ARE LIKELY TIED TO DAYTIME HEATING. SIMILAR ACTIVITY
COVERS MUCH OF PANAMA ASSOCIATED WITH THE E PACIFIC MONSOON
TROUGH THAT EXTENDS S OF THE COUNTRY TO A 1008 MB LOW OVER NRN
COLOMBIA. A FEW SCATTERED SHOWERS/THUNDERSTORMS ARE ALSO OVER
HISPANIOLA DUE TO A TROPICAL WAVE ACROSS THE ERN CARIBBEAN.
ISOLATED SHOWERS ARE E OF 66W ASSOCIATED WITH THE WAVE.THE
REMAINDER OF THE CARIBBEAN IS EXPERIENCING FAIR WEATHER DUE TO
DRY AIR ALOFT WRAPPING AROUND AN UPPER LEVEL LOW S OF CUBA NEAR
20N78W. TRADEWIND FLOW OF 20 KTS IS PRESENT OVER THE CENTRAL
CARIBBEAN WITH LIGHTER WINDS TO EITHER SIDE. EXPECT THE TROPICAL
WAVE TO CONTINUE MOVING WWD INTO THE CENTRAL AMERICA PROVIDING
MOIST CONDITIONS ACROSS THIS AREA. A LARGE AREA OF SAHARAN DUST
TRAILS BEHIND THE WAVE AND WILL LIKELY HIT THE ERN CARIBBEAN
WITHIN 24 HOURS. MOIST CONDITIONS WILL ALSO LIKELY REMAIN OVER
CENTRAL AMERICA.

ATLANTIC OCEAN...
AN UPPER LEVEL LOW CENTERED OVER ERN GEORGIA IS SUPPORTING A
LINE OF SHOWERS/THUNDERSTORMS FROM 32N76W TO 28N82W ACROSS THE
FLORIDA PENINSULA. THE REMAINDER OF THE W ATLC IS DOMINATED BY
SURFACE RIDGING AROUND A 1028 MB HIGH NEAR 34N45W PROVIDING
MOSTLY FAIR CONDITIONS. THE HIGH IS SUPPORTED BY AN UPPER LEVEL
RIDGE CENTERED NEAR 26N54W. AN UPPER LEVEL LOW IS TO THE W
CENTERED NEAR 29N65W WITH A TROUGH AXIS EXTENDING TO AN UPPER
LEVEL LOW IN THE CENTRAL CARIBBEAN. THE TROUGH AXIS IS
SUPPORTING SOME ISOLATED SHOWERS ACROSS THE ERN BAHAMAS AND THE
AREA N OF THE ERN CARIBBEAN. THE AFOREMENTIONED SURFACE HIGH IS
ALSO PROVIDING RIDGING ACROSS THE CENTRAL AND ERN ATLC WHERE
FAIR WEATHER DOMINATES. AN UPPER LEVEL TROUGH EXTENDS FROM E OF
THE AZORES ISLANDS TO NEAR 28N40W...BUT IS NOT CAUSING ANY
SIGNIFICANT WEATHER. UPPER LEVEL RIDGING ALSO COVERS THE FAR ERN
ATLC CENTERED JUST OFF THE AFRICAN COAST NEAR 17N20W. THE LAST
VISIBLE SATELLITE IMAGERY INDICATES A LARGE AREA OF SAHARAN DUST
COVERS MUCH OF THE TROPICAL ATLC AROUND THE TROPICAL
WAVES...WHICH IS HELPING SUPPORT FAIR SURFACE CONDITIONS.

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

$$
WALTON




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