000 FXCA62 TJSJ 041546 AFDSJU AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN JUAN PR 1146 AM AST SAT JUL 4 2009 .UPDATE... PATCHES OF LOW AND HIGH LEVEL CLOUDS MOVING ACROSS THE REGION... COMBINED WITH THE SAHARAN DUST SPREADING WESTWARD ACROSS THE AREA... MAINTAINED PARTLY CLOUDY AND HAZY CONDITIONS ACROSS THE ISLANDS AND SURROUNDING WATERS THIS MORNING. A FEW LIGHT SHOWERS WERE NOTED MOVING ACROSS THE COASTAL WATERS EARLIER THIS MORNING...BUT HAVE SINCE THEN DISSIPATED WITH NO PRECIPITATION OBSERVED OVER LAND. LATEST SATELLITE IMAGERY SHOWED EXPECT RELATIVE DRY AIR AND HAZY CONDITIONS SPREADING ACROSS THE REGION WITH PREVIOUSLY MENTIONED TROPICAL WAVE/TROUGH MOVING WELL SOUTH OF THE AREA AND HAVING LITTLE AFFECT ON THE LOCAL WEATHER PATTERN. LOCALLY STREAMERS HAVE BEGUN TO DEVELOP ACROSS PARTS OF THE ISLANDS...AND THE PRESENT EASTERLY WIND FLOW OF 15-20 KTS WILL PUSH THESE CLOUD LINES ACROSS THE LOCAL WATERS...AND WILL EVENTUALLY AFFECT PARTS OF THE EAST INTERIOR AND WEST SECTIONS OF PUERTO RICO DURING THE AFTERNOON. STILL EXPECT AFTERNOON CONVECTION TO BE FOCUSED IN THE WEST AND PARTS OF CENTRAL INTERIOR...BUT ONLY EXPECT QUICK BURSTS OF SHOWERS AND THUNDERSTORMS OF RELATIVELY SHORT DURATION. HOWEVER A FEW THUNDERSTORMS MAY BE FAIRLY STRONG AND CAPABLE OF PRODUCING LOCALLY HEAVY RAINFALL...GUSTY WINDS AND DANGEROUS CLOUD TO GROUND LIGHTNING DURING THE AFTERNOON. NO MAJOR CHANGES MADE TO THE INHERITED FORECAST WHICH HAD GOOD HANDLE ON PRESENT AND EXPECTED CONDITIONS FOR THE NEXT FEW DAYS...WITH SAHARAN DUST BEING THE MOST SIGNIFICANT FEATURE ACROSS THE REGION...AS WELL AS A TROPICAL WAVE NOW EXPECTED TO MOVE ACROSS THE EASTERN CARIBBEAN LATE SUNDAY INTO MONDAY. THE LATTER WILL RAISE THE CHANCES FOR SHOWERS AND THUNDERSTORM ACTIVITY ACROSS THE ISLANDS AND SURROUNDING WATERS AT LEAST THROUGH MONDAY MORNING...AS IT WILL PASS QUICKLY ACROSS THE REGION...TO BE FOLLOWED BY A RETURN OF HOT AND HAZY CONDITIONS. && .AVIATION... NO CHANGES TO PREVIOUS AVIATION DISCUSSION. && .PREV DISCUSSION... /ISSUED 312 AM AST SAT JUL 4 2009/ DISCUSSION...PATTERN PROGRESSING IN HARMONY WITH GOING FORECAST. BOTH TROPICAL WAVES HAVE MOVED ABOUT 10 DEGREES OVER THE LAST DAY...WITH WESTERN WAVE AXIS ALIGNED SOUTH OF PR AND SECOND WAVE AT ABOUT 45W. SAHARAN AIR LAYER STARTING TO CREEP INTO AREA AS LOCAL OBSERVATION AT THE OFFICE SHOW SOME MINOR HAZE AS OF 2 AM. STILL EXPECTING HAZE TO BECOME MORE DENSE TODAY...BUT MIGHT NOT SEE THE INTENSE CONCENTRATION WE WERE PREVIOUSLY EXPECTING UNTIL MONDAY. NEVERTHELESS...TO THOSE BOTHERED BY THE SAHARAN AIR MASS...YOU CAN EXPECT SOME EFFECTS THIS WEEKEND. MOSTLY DRY AIR ON BACK SIDE OF CURRENT WAVE EXPECT FOR THIS AFTERNOON...WITH ONLY DIURNALLY FORCED CONVECTION AND THE TYPICAL ISLAND STREAMERS. AFTERWARD MOISTURE ADVECTION FROM SECOND WAVE STARTS WORKING INTO THE FORECAST AREA SUNDAY MORNING...WITH BEST MOISTURE OVERNIGHT SUNDAY NIGHT INTO MONDAY. STILL KEEPING NUMEROUS POPS FOR VI AND MOST OF PR FOR SUNDAY MORNING AND SUNDAY NIGHT/MONDAY MORNING. EACH AFTERNOON SHOULD ALSO PRODUCE MORE WIDESPREAD COVERAGE AND CLOUDIER SKIES THAN THE TYPICAL DIURNAL PATTERN. NAM12 SHOWING 40 KT FLOW AT 850MB WITH PASSAGE OF WAVE AXIS SUNDAY NIGHT. WILL HAVE TO WATCH WITH SAL INTERACTION FOR GUST BOUNDARIES AND ISSUE MARINE PRODUCTS AS FIT. SCA IN PLACE FOR MOST SOUTHERN WATERS THROUGH MONDAY. AFTER WAVE AXIS PASSES MONDAY EVENING...BACK TO DRY AND DUSTY UNTIL NEXT WAVE NOW PROGGED FOR THURSDAY THROUGH NEXT WEEKEND. AVIATION...MOSTLY VFR CONDITIONS WILL PREVAIL AT ALL LOCAL TAF SITES THROUGH 03/16Z. AFT 16Z SHOWERS AND THUNDERSTORMS WILL DEVELOP OVER WEST AND NORTHWEST PUERTO RICO. MODELS SUGGEST THAT WINDS WILL SHIFT MORE NORTHEASTERLY ON THE NORTHERN COAST OF PUERTO RICO SO THAT MVFR CONDITIONS WILL OCCUR BRIEFLY IF AT ALL AT TJBQ...BUT TJMZ IS LIKELY TO SEE MVFR OR BRIEF IFR CONDITIONS IN A THUNDERSHOWER. STREAMERS OFF THE LOCAL ISLANDS MAY COMPLICATE THE FORECAST FOR TJSJ...BUT IF SHOWERS FORM THEY SHOULD REMAIN SOUTHWEST OF THE AIRPORT. A TROPICAL WAVE WILL MOVE THROUGH THE LEEWARD ISLANDS WITH TNCM AND TKPK AFTER 04/22Z AND INTO CARIBBEAN WATERS OF THE FORECAST AREA AFTER 05/00Z. THIS SHOULD SPREAD SCT-NUM SHOWERS AND THUNDERSTORMS OVER PR AND THE USVI AFTER 05/10Z DURING THE DAY SUNDAY. CONDITIONS WILL BECOME HAZIER DURING THE NEXT 24 HOURS AS SAHARAN DUST MOVES INTO THE AREA. && .PRELIMINARY POINT TEMPS/POPS... SJU 90 80 88 79 / 20 50 50 50 STT 90 79 88 79 / 30 60 60 60 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...NONE. VI...NONE. && $$ 09/04