AFDSJU AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN JUAN PR 1115 AM AST FRI JUL 8 2011 .UPDATE...ACTIVE TROPICAL WAVE ACROSS THE VIRGIN ISLANDS WITH SHOWERS AND THUNDERSTORMS. WEATHER SLOWLY SPREADING WEST NORTHWEST. PRECIPITABLE WATER VALUES AROUND 2.15 OVER THE AREA AS THE TROPICAL WAVE CONTINUES TO MOVE WESTWARD. WAVE AXIS LOCATED ACROSS WESTERN PUERTO RICO. NO CHANGE TO FORECAST GRIDS. && .DISCUSSION...TROPICAL WAVE AXIS LOCATED ACROSS WEST PUERTO RICO EARLIER TODAY WITH SOUTHEAST FLOW AND ACTIVE WEATHER BEHIND THE WAVE AXIS. VIRGIN ISLANDS GETTING HAMMERED AGAIN WITH SHOWERS AND THUNDERSTORMS. GROUNDS ACROSS USVI ARE TOTALLY SATURATED DUE TO PREVIOUS RAINFALL. URBAN AND SMALL STREAM FLOOD ADVISORIES IN EFFECT FOR THE TERRITORY AND COULD EASILY ESCALATE TO FLASH FLOOD WARNINGS LATER. WEATHER CONDITIONS WILL SLOWLY DETERIORATE OVER MAINLAND PR AS THE WEATHER SPREADS WEST NORTHWEST DURING THE REST OF TODAY. MID TO UPPER FLOW FROM THE WEST TO SOUTHWEST...WHICH IMPLIES THUNDERSTORM DEVELOP OVER THE CENTRAL INTERIOR AND SOUTHWEST WILL PUSH CB ANVILS OVER NORTH PR LATER THIS AFTERNOON. FORECAST GRIDS HAVE A GOOD HANDLE ON THE SITUATION AND SEE NO NEED FOR UPDATES. && .AVIATION... PREVAILING VFR TO MVFR CONDITIONS EXPECTED OVER PUERTO RICO TAF SITES WITH MVFR TO IFR FROM TJNR ESE TO THE USVI AND VICINITY THROUGH 23Z. PERIODS OF MVFR CONDITIONS CAN BE EXPECTED ACROSS TKPK...TNCM AND TKPK IN SHRA. AFTER 08/16Z MOISTURE WILL INCREASE WITH MVFR OR EVEN IFR CONDITIONS AND MOUNTAIN OBSCURATIONS EXPECTED OVER THE PUERTO RICO TAF SITES THROUGHOUT THE AFTERNOON IN SCATTERED TO NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS. WINDS ARE EXPECTED TO BE EAST SOUTHEAST AT 15 TO 25 MPH. && .PREV DISCUSSION... /ISSUED 521 AM AST FRI JUL 8 2011/ SYNOPSIS...AT UPPER LEVELS...A TROUGH DRAPES DOWN OVER THE DOMINICAN REPUBLIC AND HIGH PRESSURE COVERS MOST OF THE NORTHEASTERN CARIBBEAN. HIGH PRESSURE CONTINUES OVER THE CARIBBEAN THROUGH THE FIRST PART OF NEXT WEEK. BUT...THE LOW TO THE NORTHEAST SHIFTS SOUTH INTO THE TROPICAL ATLANTIC DURING THE WEEK AND THEN MOVES OVER PUERTO RICO BY THE FOLLOWING WEEKEND. AT MID LEVELS...HIGH PRESSURE CONTINUES ACROSS THE WESTERN ATLANTIC UNTIL MID WEEK WHEN AN UPPER LEVEL TROUGH NEAR 60 WEST CREATES A WEAKNESS IN THE RIDGE. AT LOWER LEVELS...A TROPICAL WAVE IS MOVING THROUGH THE EASTERN CARIBBEAN AND WILL SPREAD MOISTURE ACROSS THE LOCAL AREA. SOME AFRICAN DUST WILL FOLLOW. HIGH PRESSURE REMAINS ANCHORED IN THE NORTHEAST ATLANTIC THROUGH THE NEXT WEEK TO TEN DAYS AND WILL MAINTAIN MODERATE TO FRESH TRADE WINDS OVER THE AREA. DISCUSSION...AN AREA OF RAIN AND THUNDERSTORMS DEVELOPED OVERNIGHT AND COVERED MUCH OF THE LOCAL CARIBBEAN WATERS FROM JUST SOUTH OF THE COASTAL WATERS OFF CABO ROJO TO WELL EAST NORTHEAST OF SAINT CROIX. SOME OF THE EMBEDDED THUNDERSTORMS HAD TOPS GREATER THAN FIFTY THOUSAND FEET. SOME OF THE SHOWERS MOVED INLAND...BUT COOL SURFACE TEMPERATURES GENERALLY KILLED THESE SHOWERS. SAINT CROIX HAS BEEN UNDER MODERATE RAIN FOR QUITE SOME TIME. SHOWERS AND THUNDERSTORMS WILL CONTINUE TO DEVELOP AND MOVE NORTHWEST INTO PUERTO RICO AND TO SOME EXTENT THE NORTHERN U.S. VIRGIN ISLANDS TODAY AND TONIGHT. DUE TO EXTENSIVE CLOUD COVER...THUNDERSTORMS WILL CONTINUE TO BE SCATTERED TO ISOLATED AND THE BEST CHANCES FOR RAIN OVER LAND WILL BE IN SOUTHEAST PUERTO RICO AND OVER SAINT CROIX. AREAS OF URBAN AND SMALL STREAM FLOODING WILL ARE EXPECTED AGAIN TODAY. MODELS SHOW THE ARCHING RAIN BANDS OF THE TROPICAL WAVE PULLING AWAY FROM THE AREA ON SATURDAY. WINDS AT 850 MB NEVER DEVIATE FROM THEIR EAST TO SOUTHEAST FLOW DUE TO THE PERSISTENCE OF THE HIGH PRESSURE IN THE NORTHEAST ATLANTIC...AND THIS WILL TEND TO BRING POPS DURING THE WEEK BACK TO CLIMATOLOGY OVER MUCH OF THE AREA. THE NEXT TROPICAL WAVE RUSHES IN FROM THE SOUTHEAST ON THURSDAY...BUT IS NOT SEEN AS BEING AS STRONG AS THE WAVE MOVING THROUGH TODAY. AVIATION... PREVAILING VFR CONDITIONS ARE EXPECTED ACROSS MOST TAF SITES THROUGH AT LEAST 08/12Z. PERIODS OF MVFR CONDITIONS CAN BE EXPECTED ACROSS TKPK...TNCM AND TISX IN SHRA. AFTER 08/12Z MOISTURE WILL INCREASE WITH MVFR OR EVEN IFR CONDITIONS AND LOCAL MOUNTAIN OBSCURATIONS EXPECTED OVER THE LOCAL TAF SITES THROUGHOUT THE DAY IN SCATTERED TO NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS. WINDS ARE EXPECTED TO BE LIGHT AND VARIABLE UNTIL AFT 08/12Z...THEN SFC WINDS WILL INCREASE TO 10-15 KTS FROM THE EAST. MARINE...THE INCOMING TROPICAL WAVE WILL BRING SOMEWHAT INCREASED WINDS THAT WILL RAISE SEAS IN THE OUTER COASTAL WATERS. HENCE A SMALL CRAFT ADVISORY WAS ISSUED BEGINNING AT NOON FOR THESE WATERS. SEAS WILL SUBSIDE TOMORROW AND AFTER SUNDAY ARE NOT EXPECTED TO ATTAIN SMALL CRAFT ADVISORY INTENSITIES FOR THE REST OF THE WEEK. && .PRELIMINARY POINT TEMPS/POPS... SJU 87 77 89 78 / 80 50 50 30 STT 87 78 89 80 / 80 50 40 20 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...NONE. VI...NONE. && $$