[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 172332
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT WED JUL 17 2013

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 EXTENDS FROM 19N25W TO 8N29W MOVING W AT 15-20 KT.
THE WAVE COINCIDES WITH A LARGE SURGE OF DEEP LAYER MOISTURE
PRESENT IN TOTAL PRECIPITABLE WATER IMAGERY ALONG WITH A 700 MB
TROUGH AXIS. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS
FROM 7N-10N BETWEEN 25W-33W.

TROPICAL WAVE EXTENDS FROM 21N60W TO 13N62W MOVING W AT 20-25
KT. THE WAVE LIES WITHIN AN AREA OF ENHANCED MOISTURE EVIDENT IN
TOTAL PRECIPITABLE WATER IMAGERY...AND HAS ESCAPED THE DRY
SAHARAN AIR LAYER PRESENT OVER MUCH OF THE TROPICAL ATLC. THIS
HAS LED TO INCREASED CONVECTION NEAR THE WAVE OVER THE PAST 24
HOURS. CURRENTLY...SCATTERED MODERATE/ISOLATED STRONG CONVECTION
IS FROM 14N-17N BETWEEN 59W-62W. ISOLATED MODERATE CONVECTION IS
FROM 18N-21N BETWEEN 57W-62W.

TROPICAL WAVE EXTENDS FROM 18N74W TO 11N75W MOVING W AT 20 KT.
THE MOISTURE SIGNAL WITH THE WAVE HAS WEAKENED CONSIDERABLY WITH
ONLY A WEAK INCREASE IN MOISTURE TO THE WEST OF THE AXIS. THE
WAVE ALSO ALIGNS WITH A VERY WEAK SIGNAL IN THE 700 MB FIELDS
WHICH IS MOST PROMINENT NEAR THE COAST OF COLOMBIA. ONLY A
SMALL CLUSTER OF STRONG CONVECTION IS OVER HAITI FROM 19N-20N
BETWEEN 72W-73W.

...ITCZ/MONSOON TROUGH...
THE MONSOON TROUGH EXTENDS FROM THE COAST OF MAURITANIA FROM
17N16W TO 19N22W. THE ITCZ BEGINS ON THE WEST SIDE OF A TROPICAL
WAVE ALONG 8N31W 6N43W 4N52W. SCATTERED MODERATE/STRONG
CONVECTION IS FROM 4N-8N BETWEEN 39W-50W.

...DISCUSSION...

GULF OF MEXICO...
A PAIR OF UPPER LEVEL LOWS DOMINATE THE UPPER LEVEL PATTERN OVER
THE GULF OF MEXICO. THE FIRST IS CENTERED OVER THE NE GULF NEAR
29N84W PROVIDING DIFFLUENT FLOW ACROSS FLORIDA. IT ALSO SUPPORTS
A WEAK SURFACE TROUGH ALONG 28N78W TO 25N82W. CURRENTLY SHOWERS
AND THUNDERSTORMS ARE JUST OFF THE WEST COAST OF THE PENINSULA
FROM 27N-29N BETWEEN 83W-85W. RADAR IMAGERY ALSO INDICATES HEAVY
SHOWERS ARE FROM 27N-28N BETWEEN 80W-81W. THE SECOND UPPER
LOW...MUCH WEAKER THAN THE FIRST...IS TO THE SOUTH NEAR 22N90W
PROVIDING DIFFLUENT ALOFT OVER THE YUCATAN PENINSULA. SCATTERED
SHOWERS/THUNDERSTORMS ARE THROUGHOUT THE PENINSULA AND ACROSS
MUCH OF THE REST OF MEXICO AS WELL. SHOWERS/THUNDERSTORMS ARE
ALSO MOVING THROUGH THE NW GULF TOWARDS TEXAS ASSOCIATED WITH
ANOTHER AREA OF DIFFLUENT FLOW ALOFT ASSOCIATED WITH AN UPPER
LEVEL LOW OVER NEW MEXICO. AT THE SURFACE...BROAD RIDGING IS
THROUGHOUT EXTENDING FROM A HIGH CENTER OVER ILLINOIS. THIS
PATTER IS PROVIDING MAINLY EAST TO SOUTHWEST FLOW OF 10-15 KT
WITH A FEW 20 KT WINDS OVER THE NORTH CENTRAL GULF. THE SURFACE
TROUGH OVER FLORIDA IS EXPECT TO SLOWLY DRIFT WESTWARD THROUGH
THE END OF THE WEEK BEFORE DISSIPATING INLAND OVER THE WEEKEND.
THE STRONG UPPER LOW OVER FLORIDA IS ALSO EXPECTED TO DRIFT WEST
WHICH WILL PROVIDE A WIDE AREA OF DIFFLUENCE OVER THE
EASTERN/CENTRAL GULF LEADING TO SHOWERS/THUNDERSTORMS.

CARIBBEAN SEA...
WEAK UPPER RIDGING IS OVER THE WESTERN CARIBBEAN. DIFFLUENT FLOW
WEST OF THE UPPER RIDGE IS SUPPORTING HEAVY
SHOWERS/THUNDERSTORMS OVER BOTH THE NW CARIBBEAN AND THROUGHOUT
CENTRAL AMERICA. ACTIVITY OVER THE NW CORNER IS FROM 19N-22N
BETWEEN 80W-87W CONTINUING OVER MUCH OF CUBA. ACTIVITY OVER
CENTRAL AMERICA IS MAINLY BETWEEN 84W-88W WITH THE STRONGEST
ACTIVITY OVER COSTA RICA. ACTIVITY ALSO CONTINUES THROUGH PANAMA
ASSOCIATED WITH THE MONSOON TROUGH EXTENDING ALONG 10N TO A 1008
MB SURFACE LOW OVER NORTHERN COLOMBIA. FARTHER EAST...TWO
TROPICAL WAVES ARE MOVING THROUGH THE BASIN. THE FIRST IS ALONG
75W...BUT IS NOT ACCOMPANIED BY MUCH MOISTURE LEAVING THIS
PORTION OF THE BASIN FAIRLY DRY. DRY AIR ALOFT AROUND A BROAD
UPPER TROUGH ALONG 70W IS ALSO CONTRIBUTING TO THE FAIR WEATHER.
THE SECOND WAVE IS MOVING THROUGH THE LESSER ANTILLES PROVIDING
SCATTERED SHOWERS/ISOLATED THUNDERSTORMS NORTH OF 13N EAST OF
69W. TRADEWIND FLOW OF 15-25 KT IS THROUGHOUT MUCH OF THE AREA
WITH THE STRONGEST WINDS IN THE CENTRAL CARIBBEAN. THE WAVE IN
THE CENTRAL CARIBBEAN WILL CONTINUE TO MOVE WEST...BUT WILL
LIKELY DISSIPATE SOON. THE SECOND WAVE SHOULD CONTINUE THROUGH
THE EASTERN CARIBBEAN INTO THE CENTRAL CARIBBEAN PRODUCING
SCATTERED SHOWERS...SOME HEAVY AT TIMES.

HISPANIOLA...
ONLY A SMALL CLUSTER OF SHOWERS/THUNDERSTORMS IS OVER HAITI FROM
19N-20N BETWEEN 72W-73W. THIS IS LIKELY A RESULT OF DAYTIME
HEATING WITH LITTLE INFLUENCE FROM THE WEAK TROPICAL WAVE TO THE
WEST. A SECOND STRONGER TROPICAL WAVE IS EXPECTED TO REACH THE
ISLAND WITHIN THE NEXT 24 HOURS AND WILL INCREASE MOISTURE AND
CONVECTION.

ATLANTIC OCEAN...
THE UPPER LEVEL LOW OVER THE EASTERN GULF OF MEXICO IS PROVIDING
DIFFLUENCE ALOFT OVER THE WEST ATLC SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS FROM 23N-28N BETWEEN 74W-78W. A WEAK UPPER
RIDGE IS ALONG 76W WHILE AN ELONGATED UPPER LOW IS FARTHER EAST
SUPPORTING A SURFACE TROUGH FROM 30N67W TO 26N70W. ISOLATED
SHOWERS/THUNDERSTORMS ARE FROM 29N-30N BETWEEN 65W-68W. THE
REMAINDER OF THE BASIN IS DOMINATED BY BROAD SURFACE RIDGING
ANCHORED BY A 1025 MB HIGH NEAR 28N44W. THE RIDGE IS SUPPORTED
BY BROAD UPPER RIDGING CENTERED NEAR 20N31W. A DRY SAHARAN AIR
LAYER ALSO COVERS MUCH OF THE TROPICAL ATLC FROM THE COAST OF
AFRICA AROUND THE TROPICAL WAVE TO NEAR 50W.

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

$$
WALTON


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