[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 062345
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SAT OCT 06 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 EXTENDS FROM 17N28W TO 9N27W MOVING W AT 15 KT.
THE WAVE IS EMBEDDED WITHIN BROAD CYCLONIC FLOW AROUND THE
MONSOON TROUGH THAT IS CENTERED NEAR THE SOUTHERN EXTENT OF THE
WAVE WHERE A SPOT 1010 MB SURFACE LOW HAS BEEN ANALYZED. THE
WAVE LIES ON THE WESTERN SIDE OF A SURGE OF DEEP LAYER MOISTURE
PRESENT IN TOTAL PRECIPITABLE WATER IMAGERY. CONVECTION IS
CURRENTLY RESTRICTED TO THE MONSOON TROUGH REGION NEAR THE LOW
PRESSURE CENTER. SCATTERED MODERATE/ISOLATED STRONG CONVECTION
IS FROM 3N-9N BETWEEN 24W-28W...AND FROM 7N-11N BETWEEN 28W-34W.

TROPICAL WAVE IN THE CENTRAL CARIBBEAN IS FROM 18N69W TO 12N70W
MOVING W AT 15-20 KT. THE WAVE IS LARGELY AN EXTENSION OF
LOW-LEVEL TROUGHING FROM A 1007 MB SURFACE LOW CENTERED NORTH OF
THE MONA PASSAGE NEAR 22N67W COMBINED WITH ENERGY THAT HAS
ROTATED AROUND THE PERIPHERY OF A MID-LEVEL RIDGE ANCHORED OVER
THE SW NORTH ATLC DURING THE PAST WEEK. ONLY A FEW
SHOWERS/THUNDERSTORMS ARE OVER HISPANIOLA AT THE NORTHERN EXTENT
OF THE WAVE. LARGE CLUSTERS OF STRONG CONVECTION ARE TO THE
SOUTH OVER VENEZUELA.

TROPICAL WAVE EXTENDS FROM THE NW CARIBBEAN AT 19N84W TO THE SW
CARIBBEAN AT 11N78W MOVING W AT 15-20 KT. THE WAVE IS EMBEDDED
WITHIN AN AREA OF DEEP LAYER MOISTURE ACROSS THE SW CARIBBEAN
MOSTLY SOUTH OF 14N AS INDICATED BY TOTAL PRECIPITABLE WATER
IMAGERY. THE SOUTHERN PORTION OF THE WAVE IS ALSO EMBEDDED
WITHIN BROAD MONSOONAL FLOW AS THE E PACIFIC MONSOON TROUGH
EXTENDS ACROSS COSTA RICA TO THE BASE OF THE WAVE. SCATTERED
MODERATE CONVECTION IS FROM 10N-12N BETWEEN 77W-81W.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS ACROSS WEST AFRICA TO THE COAST OF
GUINEA-BISSAU AT 12N16W CONTINUING TO THE BASE OF A TROPICAL
WAVE AT 9N27W AND ALONG 10N36W 9N42W. MOST OF THE CONVECTION
NEAR THE MONSOON TROUGH HAS BEEN TIED TO THE TROPICAL WAVE. A
LARGE CLUSTER OF MODERATE/STRONG CONVECTION IS ALSO MOVING OFF
THE COAST OF AFRICA FROM 7N-11N BETWEEN 9W-14W. A CLUSTER OF
STRONG CONVECTION IS ALSO FROM 4N-6N BETWEEN 19W-21W.

...DISCUSSION...

GULF OF MEXICO...
MAINLY WESTERLY FLOW ALOFT COVERS THE MAJORITY OF THE GULF OF
MEXICO AROUND THE BASE OF A BROAD UPPER LEVEL TROUGH COVERING
MUCH OF THE UNITED STATES. A WEAK SHORTWAVE TROUGH EXTENDS DOWN
THE EXTREME WESTERN EDGE OF THE BASIN NEAR THE MEXICO COAST
SUPPORTING SCATTERED SHOWERS/ISOLATED THUNDERSTORMS IN THE SW
GULF FROM 18N-22N BETWEEN 91W-96W. SIMILAR ACTIVITY ALSO COVERS
MUCH OF THE SOUTHEASTERN GULF AS WELL DUE TO MORE MOIST
SOUTHWESTERLY FLOW ALOFT ACROSS THIS PORTION OF THE BASIN. SOME
STRONGER SHOWERS/THUNDERSTORMS ARE ACROSS THE FLORIDA PENINSULA
NEAR A DIURNAL SURFACE TROUGH THAT HAS FORMED OVER THE PENINSULA
DUE TO SEABREEZE CONVERGENCE. THE NORTHERN GULF IS MOSTLY DRY
AND CLEAR DUE TO STRONG DRY AIR AND SUBSIDENCE ALOFT. DESPITE
BROAD SURFACE RIDGING ACROSS MUCH OF THE UNITED STATES...A
FRONTAL BOUNDARY IS APPROACHING THE BASIN AND IS CURRENTLY JUST
INLAND OF THE GULF COAST. IT IS STATIONARY FOR THE TIME BEING
DUE TO THE BROADNESS OF THE UPPER TROUGH. HOWEVER...AS A
SHORTWAVE TROUGH MOVES THROUGH THE LONGWAVE IT WILL GIVE THE
FRONT ENOUGH PUSH TO MAKE INTO THE BASIN LIKELY IN THE OVERNIGHT
HOURS. IT MOST LIKELY WILL NOT BE A VERY MOIST FRONT DUE TO THE
ABUNDANCE OF DRY AIR IN THE AREA...BUT STRONGER WINDS ARE
EXPECTED BEHIND THE FRONT. SURFACE RIDGING WILL BUILD IN BEHIND
IT.

CARIBBEAN SEA...
AN UPPER LEVEL RIDGE COVERS THE NW CARIBBEAN CENTERED OVER
HONDURAS AND NICARAGUA NEAR 15N84W. THE RIDGE IS DRAWING MOIST
AIR AROUND ITS WESTERN SIDE...WHILE DRY AIR REMAINS OVER THE
EASTERN SIDE. THIS PATTERN IS PRODUCING ISOLATED
SHOWERS/THUNDERSTORMS ACROSS MUCH OF CENTRAL AMERICA...BUT IS
INHIBITING CONVECTION NEAR THE NORTHERN HALF OF A TROPICAL WAVE
THAT EXTENDS FROM THE NW CARIBBEAN INTO THE SW CARIBBEAN. THE
SOUTHERN HALF OF THE WAVE IS PRODUCING SHOWERS/THUNDERSTORMS AS
IT IS EMBEDDED WITHIN THE BROAD CYCLONIC FLOW AROUND THE MONSOON
TROUGH THAT EXTENDS FROM SOUTHERN COSTA RICA TO THE BASE OF THE
WAVE. SEE TROPICAL WAVE SECTION FOR MORE DETAILS. A SECOND
TROPICAL WAVE IS IN THE CENTRAL CARIBBEAN...BUT IS NOT CAUSING
MUCH SIGNIFICANT WEATHER. BROAD UPPER TROUGHING COVERS THE
REMAINDER OF THE BASIN...BUT IT IS DRAWING IN DRY AIR AROUND ITS
EASTERN SIDE...WHICH IS KEEPING MUCH OF THE CENTRAL AND EASTERN
CARIBBEAN UNDER FAIR CONDITIONS. HOWEVER...STRONG CONVECTION
CONTINUES OVER NORTHERN COLOMBIA AND NORTHERN VENEZUELA. ONLY A
FEW ISOLATED SHOWERS HAVE POPPED UP OF THE LESSER ANTILLES. BOTH
WAVES WILL CONTINUE WESTWARD.

ATLANTIC OCEAN...
MOIST DIFFLUENT FLOW IS ACROSS THE FAR WESTERN ATLC SUPPORTING
SCATTERED SHOWERS/ISOLATED THUNDERSTORMS WEST OF 74W TO THE
FLORIDA COAST AND NORTH OF 26N. A WEAK UPPER RIDGE EXTENDS
ACROSS THE BAHAMAS...BUT A SMALL SHORTWAVE TROUGH IS IMMEDIATELY
TO THE EAST ASSOCIATED WITH AN UPPER LEVEL LOW NE OF THE LESSER
ANTILLES NEAR 22N60W. THE SHORTWAVE IS SUPPORTING A 1007 MB
SURFACE LOW NEAR 22N67W ALONG WITH SCATTERED SHOWERS/ISOLATED
THUNDERSTORMS FROM 21N-27N BETWEEN 66W-72W. A WEAK SURFACE
TROUGH IS ANALYZED UNDERNEATH THE UPPER LOW FROM 22N58W TO
19N61W. SCATTERED SHOWERS/THUNDERSTORMS ARE FROM 20N-22N BETWEEN
58W-60W. SCATTERED SHOWERS/ISOLATED THUNDERSTORMS ARE FROM
17N-21N BETWEEN 52W-57W. AN UPPER LEVEL RIDGE COVERS THE
MAJORITY OF THE TROPICAL ATLC CENTERED NEAR 16N42W. IT SUPPORTS
A WEAK 1012 MB SURFACE HIGH CENTERED NEAR 17N50W. THE PRESENCE
OF THIS RIDGE IS ALSO INHIBITING THE PRESENCE OF AN ATLANTIC
ITCZ AT THIS TIME. A BROAD UPPER LEVEL TROUGH COVERS MUCH OF THE
NE ATLC SUPPORTING A COLD FRONT THAT ENTERS THE DISCUSSION AREA
NEAR 32N26W AND CONTINUES ALONG 23N40W 24N50W. IT THEN BECOMES
STATIONARY TO 26N60W AND DISSIPATING TO 24N66W AS IT WRAPS
AROUND THE UPPER LOW NORTH OF THE CARIBBEAN. ISOLATED SHOWERS
ARE WITHIN 120 NM AHEAD OF THE COLD PORTION OF THE FRONT...AND
WITHIN 90 NM EITHER SIDE THE AXIS ALONG THE REMAINDER OF THE
FRONT.

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

$$
WALTON





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