000 AXNT20 KNHC 182339 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT WED JUL 18 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 ADJUSTED FARTHER W TO ALIGN WITH A WEAK 1014 MB SURFACE LOW EMBEDDED WITHIN THE MONSOON TROUGH AT 12N33W. THE WAVE EXTENDS FROM THE LOW CENTER TO 18N33W. DUE TO THE APPEARANCE OF THE LOW IT IS HARD TO DETERMINE THE CURRENT MOTION OF THE WAVE...BUT IT IS LIKELY AROUND 10-15 KT TO THE W. A LARGE AREA OF SAHARAN DUST SURROUNDS THE WAVE TO THE N AND IS LIMITING CONVECTION NEAR IT. SCATTERED MODERATE CONVECTION IS NEAR THE LOW CENTER AND TO THE W. THE CONVECTION TO THE W WILL BE DESCRIBED IN THE MONSOON TROUGH SECTION. TROPICAL WAVE IS ALONG 18N58W TO 12N55W MOVING W NEAR 15-20 KT. 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. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS W OF THE WAVE FROM 15N-19N BETWEEN 57W-60W. TROPICAL WAVE APPROACHES THE YUCATAN PENINSULA ALONG 23N86W TO 16N87W MOVING W AT 15 KT. THE WAVE LIES WITHIN A LARGE AREA OF DEEP LAYER MOISTURE THAT WAS PREVIOUSLY ACROSS THE NW CARIBBEAN AND HAS NOW SHIFTED ACROSS THE YUCATAN AND GULF OF MEXICO. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS MOSTLY W OF THE WAVE AXIS FROM 16N-21N BETWEEN 87W-91W. SIMILAR ACTIVITY IS TO THE S COVERING HONDURAS. AN UPPER LEVEL LOW OVER THE NW YUCATAN IS ALSO ENHANCING SOME OF THIS CONVECTION. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS ACROSS W AFRICA TO THE COAST OF SENEGAL AT 15N17W CONTINUING TO A 1014 MB LOW AT 12N33W...AND ALONG 8N40W 9N49W. THE ITCZ BEGINS AT 9N49W CONTINUING TO 9N62W. SCATTERED MODERATE CONVECTION IS FROM 10N-14N BETWEEN 23W-27W...AND FROM 7N-12N BETWEEN 35W-44W. ...DISCUSSION... GULF OF MEXICO... A PAIR OF UPPER LEVEL LOWS CONTINUE TO IMPACT THE GULF OF MEXICO TONIGHT SUPPORTING LARGE AREAS OF SHOWERS/THUNDERSTORMS. THE FIRST UPPER LOW IS CENTERED OVER ERN GEORGIA NEAR 33N82W SUPPORTING A SURFACE TROUGH FROM 31N83W TO 27N85W. THE UPPER LOW HAS SHIFTED N FROM ITS POSITION AT THIS TIME YESTERDAY...WHICH HAS DRAWN THE MOISTURE TO THE N ALLOWING DRIER CONDITIONS OVER THE SE GULF. THE NE GULF IS STILL MOIST WITH SHOWERS/THUNDERSTORMS ALONG THE SURFACE TROUGH AXIS AS WELL AS ACROSS MUCH OF CENTRAL FLORIDA. A LARGE AREA OF STRONG SHOWERS/THUNDERSTORMS IS ALSO OVER SRN MISSISSIPPI AND ALABAMA. A FEW ISOLATED SHOWERS/THUNDERSTORMS ALSO LINGER IN THE CENTRAL GULF. THE SECOND UPPER LEVEL LOW IS CENTERED OVER THE NW YUCATAN PENINSULA NEAR 20N90W. IT IS ENHANCING CONVECTION NEAR A TROPICAL WAVE APPROACHING THE PENINSULA. THE CONVECTION IS LIMITED TO LAND EXCEPT FOR A SMALL AREA OF THE WRN COAST. A FEW SHOWERS/THUNDERSTORMS ARE ALSO ALONG THE MEXICAN COAST IN THE FAR WRN GULF ASSOCIATED WITH A THIRD UPPER LEVEL LOW OVER N CENTRAL MEXICO. 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 1018 MB HIGH OVER LOUISIANA. THE UPPER LOWS ARE EXPECTED TO REMAIN SOMEWHAT STATIONARY AND WILL LIKELY KEEP THE NERN GULF AND YUCATAN PENINSULA UNDER MOIST CONDITIONS FOR AT LEAST THE NEXT 24 HOURS. CARIBBEAN SEA... THE UPPER LEVEL LOW OVER THE NRN YUCATAN PENINSULA ALONG WITH THE TROPICAL WAVE JUST E OF THE PENINSULA IS SUPPORTING STRONG SHOWERS/THUNDERSTORMS ACROSS MUCH OF NRN CENTRAL AMERICA INCLUDING BELIZE...GUATEMALA...HONDURAS...AND NICARAGUA. SHOWERS/THUNDERSTORMS ARE ALSO ACROSS COSTA RICA AND PANAMA ASSOCIATED WITH THE E PACIFIC MONSOON TROUGH THAT EXTENDS S OF BOTH COUNTRIES TO A 1008 MB LOW OVER NRN COLOMBIA. A FEW ISOLATED SHOWERS/THUNDERSTORMS ARE OVER CUBA AND HISPANIOLA. THE ACTIVITY OVER HISPANIOLA IS TIED TO A MOSTLY DRY UPPER LEVEL LOW CENTERED NEAR THE SW SIDE OF THE ISLAND. THE REMAINDER OF THE CARIBBEAN IS EXPERIENCING FAIR WEATHER DUE TO DRY AIR ALOFT AROUND AN UPPER LEVEL RIDGE OVER THE SW CARIBBEAN AND THE UPPER LOW OVER HISPANIOLA. A LARGE AREA OF SAHARAN DUST IS ALSO PRESENT ACROSS THE CENTRAL AND ERN CARIBBEAN EVIDENT IN SATELLITE IMAGERY AND SURFACE OBSERVATIONS. TRADEWIND FLOW OF 20-25 KTS IS PRESENT OVER THE CENTRAL CARIBBEAN WITH LIGHTER WINDS TO EITHER SIDE. EXPECT THE TROPICAL WAVE TO CONTINUE MOVING WWD OUT OF THE NW CARIBBEAN. MOIST CONDITIONS WILL LIKELY REMAIN OVER CENTRAL AMERICA. ATLANTIC OCEAN... AN UPPER LEVEL LOW CENTERED OVER ERN GEORGIA IS SUPPORTING A FEW ISOLATED SHOWERS OFF THE NE COAST OF FLORIDA. THE REMAINDER OF THE W ATLC IS DOMINATED BY SURFACE RIDGING AROUND A 1024 MB HIGH NEAR 29N67W PROVIDING MOSTLY FAIR CONDITIONS. THE HIGH IS SUPPORTED BY AN UPPER LEVEL RIDGE CENTERED NEAR 31N72W. AN UPPER LEVEL TROUGH IS TO THE E ALONG 30N62W TO AN UPPER LEVEL LOW IN THE CENTRAL CARIBBEAN. THE UPPER TROUGH SUPPORTS SOME ISOLATED SHOWER/POSSIBLE THUNDERSTORMS FROM 120 NM EITHER SIDE OF A LINE FROM HISPANIOLA TO 29N62W. THE ERN ATLC IS COVERED BY SURFACE RIDGING ANCHORED BY A PAIR OF 1030 MB AZORES HIGHS...WHICH ARE PROVIDING FAIR WEATHER ACROSS THE REMAINDER OF THE BASIN. THE SURFACE RIDGE IS SUPPORTED BY AN UPPER LEVEL RIDGE COVERING MUCH OF THE TROPICAL ATLC CENTERED NEAR 23N52W. 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. 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