000 AXPZ20 KNHC 310938 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 1005 UTC WED JUL 31 2013 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. THE FOLLOWING INFORMATION IS BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL ANALYSIS. BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0930 UTC. ...SPECIAL FEATURES... TROPICAL STORM GIL AT 13.3N 118.9W AT 31/0900 UTC MOVING W-NW OR 285 DEG AT 13 KT. MAXIMUM SUSTAINED WINDS ARE 45 KT WITH GUSTS TO 55 KT WITH A RECENT SCATTEROMETER PASS INDICATING THAT THE RADIUS OF 34 KT WINDS IS EXPANDING OR THE N SEMICIRCLE. CURRENTLY NUMEROUS STRONG CONVECTION IS OBSERVED IN BANDS WITHIN 60 NM OF CENTER. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS NOTED ELSEWHERE WITHIN 120 NM OF LINE FROM 15N115W TO 13N120W. GIL IS EXPECTED TO MOVE WESTWARD FOR THE NEXT FEW DAYS ALONG THE SOUTHERN PERIPHERY OF A LARGE UPPER LEVEL ANTICYCLONE WHICH WILL PROVIDE FAVORABLE CONDITIONS FOR INTENSIFICATION. THIS TRACK IS ALSO ACROSS WARM SEAS SURFACE TEMPERATURES SO GIL IS FORECAST TO BECOME A MINIMAL HURRICANE ON THU. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP2/WTNT22 KNHC FOR ADDITIONAL DETAILS. A 1009 MB LOW PRESSURE IS CENTERED NEAR 12N110.5W AND IS MOVING W AT 10 KT. CURRENTLY SCATTERED MODERATE CONVECTION IS NOTED WITHIN 45 NM EITHER SIDE OF A LINE FROM 14.5N111W TO 11.5N111W. THIS LOW MAY DEVELOP INTO A TROPICAL CYCLONE AS IT MOVES W-NW TO NEAR 12.5N113.5W LATE TONIGHT...AND NEAR 13N117W ON THU NIGHT ACCOMPANIED BY CYCLONIC WINDS OF 20-30 KT AND SEAS 7-11 FT WITHIN ABOUT 120 NM N AND 60 NM S SEMICIRCLES OF THE CENTER. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS W ALONG 10N FROM THE NW COAST OF COLOMBIA AT 10N75W TO THE PACIFIC COAST OF COSTA RICA AT 11N85W TO 10N90W...THEN DIPS SW TO 09N96W...THEN NW THROUGH THE EMBEDDED SURFACE LOW PRESSURE AT 12N110.5W AND LOSING IDENTITY NEAR 12N113W IN THE BROAD CYCLONIC CIRCULATION ASSOCIATED WITH TROPICAL CYCLONE GIL. A SURFACE LOW ESTIMATED AT 1012 MB IS ANALYZED AT 12N126W WITH SCATTEROMETER WINDS INDICATED THE INTERTROPICAL CONVERGENCE ZONE FORMS SW OF THE LOW AND CONTINUES SW TO 12N127W TO 10N133W THEN TURNS W TO BEYOND 10N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS OBSERVED WITHIN 60 NM EITHER SIDE OF LINES FROM 07N77W TO 07N83W AND FROM 06N91W TO 11N107W. ISOLATED MODERATE TO STRONG CONVECTION IS NOTED WITHIN 90 NM EITHER SIDE OF A LINE FROM 14N122W TO 14N127W TO 12N130W TO 14N134W TO 13N140W...AND ALONG 07.5N BETWEEN 131-137W. SCATTERED MODERATE ISOLATED STRONG CONVECTION...ACCOMPANIED BY FREQUENT LIGHTNING...IS OBSERVED IN CLUSTERS WITHIN 150 NM OF THE COAST OF MEXICO AT 95W...99W...105W AND WITHIN ALSO WITHIN 90 NM OF 21.5N106W. ...DISCUSSION... THE MEAN AXIS OF AN UPPER TROUGH EXTENDS FROM 32N132W THROUGH UPPER CYCLONES AT 26N137W AND 18N135W...THEN CONTINUES SW TO BEYOND 15N140W. A LARGE UPPER ANTICYCLONE HAS BEEN QUASI- STATIONARY OVER THE TEXAS PANHANDLE FOR THE PAST FEW DAYS WITH AN UPPER RIDGE CURRENTLY EXTENDING SW ACROSS THE CENTRAL BAJA CALIFORNIA PENINSULA TO A SHARP CREST OVER THE DEEP TROPICAL PACIFIC AT 14N135W. DRY UPPER AIR IS INDICATED TO THE W OF THIS RIDGE AND EXTENDS W THROUGH THE UPPER TROUGH. THE ENVELOPE OF ANTICYCLONIC FLOW EXTENDS S OVER THE DISCUSSION AREA TO THE N OF 22N BETWEEN 105-121W. UPPER DEBRIS MOISTURE...FROM PREVIOUS CONVECTION ALONG THE NORTHERN SIERRA MADRE OCCIDENTAL AND OVER NW OLD MEXICO...IS ADVECTED W ACROSS THE GULF OF CALIFORNIA AND THE BAJA PENINSULA ROUGHLY TO THE N OF 26N AND REACHES NEAR 26N120W BEFORE EVAPORATING. SOME OF THIS UPPER MOISTURE IS ALSO ADVECTED N...AND LATER NE WITHIN THE UPPER RIDGE...THEN E ACROSS SOUTHERN ARIZONA...NEW MEXICO AND TEXAS. A SMALL UPPER CYCLONE IS EMBEDDED WITH THE UPPER ANTICYCLONIC FLOW NEAR 19N115W...AND CONTINUES TO MOVE W WITHIN THE UPPER EASTERLY FLOW WHILE TROPICAL CYCLONE GIL LOCATED FURTHER TO THE S PROGRESSES W ALONG THE SOUTHERN EXTENT OF THE UPPER ANTICYCLONIC FLOW. AN UPPER ANTICYCLONE IS CENTERED NEAR 15N104W AND ANOTHER IS CENTERED OVER GUATEMALA WITH THEIR COMBINED ENVELOPE OF ANTICYCLONIC FLOW EXTENDING S OVER THE TROPICS TO THE N OF 04N BETWEEN 83-114W. THE ASSOCIATED UPPER DIFFLUENCE IS SUPPORTING THE CONVECTION PREVIOUSLY DESCRIBED ALONG AND TO THE S OF THE EASTERN PORTION OF THE MONSOON TROUGH. INTENSE CONVECTION HAS DEVELOPED AGAIN THIS MORNING ALONG WESTERN COLOMBIA AND ACROSS THE GULF OF PANAMA AS PREVIOUSLY DESCRIBED. ANOTHER STRONG CLUSTER HAS FORMED ALONG THE MONSOON TROUGH AND IS MOVING W ACROSS THE COASTS RICA AND NICARAGUA BORDER AT THE MOMENT. A SURFACE RIDGE EXTENDS FROM 32N140W TO 18N108W. NE TRADES AT 15- 20 KT ARE ENHANCED SW OF THE RIDGE FROM 14-16N TO THE W OF 138W. MIXING NE AND SE SWELL RESULT IN COMBINED SEAS OF 6-8 FT. THESE CONDITIONS ARE FORECAST TO SPREAD E ACROSS THE TROPICAL WATERS FROM 12-18N TO THE W OF 131W ON THU...THEN SUBSIDE IN ADVANCE OF TROPICAL CYCLONE GIL ON FRI WHICH WILL INCREASE THE SEAS TO 8-12 FT WITHIN 330 NM E AND WITHIN 210 NM OVER THE W SEMICIRCLES OF CENTER. $$ NELSON