180 FXHW60 PHFO 151330 AFDHFO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HONOLULU HI 400 AM HST MON JUL 15 2013 .SYNOPSIS... LIGHT EAST TO SOUTHEAST WINDS WILL BECOME MORE EASTERLY AND INCREASE SLIGHTLY THROUGH THE WEEK. SHOWERS ALSO WILL BECOME HEAVIER ACROSS MUCH OF THE STATE AROUND TUESDAY...AND THEN AGAIN OVER THE WEEKEND. && .DISCUSSION... SURFACE OBSERVATIONS AROUND THE MAIN HAWAIIAN ISLANDS REPORTED LIGHT WINDS WITH A BIT OF A SOUTH VECTOR COMPONENT ACROSS MOST OF THE STATE...AND SOUNDING DATA SHOWED THIS COMPONENT PRESENT THROUGH THE DEPTH OF SURFACE MIXED LAYER. SURFACE SPEEDS REMAINED HIGHER IN THE ALENUIHAHA CHANNEL. PRESSURE TRENDS WERE MIXED...SUGGESTING LITTLE CHANGE THROUGH THE SHORT RUN. ALTHOUGH THE AIR MASS WAS ON THE DRY SIDE OF AVERAGE FOR THE SEASON...IT HAD MOISTENED SLIGHTLY OVERNIGHT...AND SATELLITE ESTIMATES OF PRECIPITABLE WATER SHOWED THE AIR MASS UPWIND HOLDING CLOSE-TO-TYPICAL AMOUNTS OF WATER VAPOR. RADAR DATA ALSO REPORTED CONSIDERABLE SHOWER ACTIVITY. EXISTING POPS WERE ADEQUATE FOR MOST WINDWARD ZONES...BUT PERSISTENT SHOWERS ALONG WEST SHORES OF THE BIG ISLAND REQUIRED A BOOST. QPF ALSO HAS BEEN INCREASED ACROSS THE STATE. ALOFT...A LARGE LOW SPRAWLED TO THE NORTHWEST OF THE STATE...AND A WEAKER HIGH TO THE EAST...BUT THE LOCAL GRADIENT WAS NEARLY FLAT. GUIDANCE PREDICTED THIS INDIFFERENT CONDITION TO PERSIST THROUGH MUCH OF THE FORECAST PERIOD...AS A SERIES OF RETROGRADING LOWS PASS BY TO THE NORTH OF THE ISLANDS...BUT PRODUCE LITTLE NET CHANGE AT MID-LEVELS OVERHEAD. THE SUBTROPICAL RIDGE AT THE SURFACE TO THE NORTH WILL REBUILD SOMEWHAT FROM ITS CURRENT MINIMUM...BUT ALL THE COMMOTION OVER IT WILL KEEP IT FROM STRENGTHENING MUCH. THUS...MODEST TRADE WINDS WILL RETURN...AND THEN PREVAIL. GUIDANCE BROADLY SUPPORTED THE ARRIVAL OF A SLIGHTLY MOISTER AIR MASS AROUND TUESDAY...AND THEN AGAIN FROM FRIDAY INTO THE WEEKEND... BUT BY EARLY NEXT WEEK THE GREATEST CONCENTRATIONS OF WATER VAPOR SHOULD BECOME LIMITED TO AROUND THE BIG ISLAND. CURRENT CONDITIONS DESPITE THE DRY AIR MASS SUGGEST THAT...CONTRARY TO EARLIER PHILOSOPHY...EACH OF THE NEW MOISTURE FLUXES COULD AFFECT MORE THAN JUST THE USUAL WINDWARD SLOPES. TYPICALLY PREFERRED AREAS LIKELY WILL REMAIN FAVORED...MEANING THAT ONCE AGAIN THE BIGGEST CHANGE FROM USUAL CONDITIONS WILL BE NOT SO MUCH IN RAINFALL DISTRIBUTION...BUT IN AMOUNTS. THUS...QPF ALSO HAS BEEN INCREASED THROUGH THE MIDDLE AND END OF THE FORECAST PERIOD. IF MODEL TRENDS CONTINUE...THEN POPS MAY NEED A BOOST STATEWIDE AS WELL. && .MARINE... SMALL SOUTH SWELLS WILL CONTINUE TODAY...BUT A MODERATE SOUTH SWELL WILL BUMP UP THE SURF TUESDAY WITH SURF APPROACHING ADVISORY LEVELS ON WEDNESDAY AS THE SWELL PEAKS. A SMALL CRAFT ADVISORY IS UP FOR THE ALENUIHAHA CHANNEL. && .HFO WATCHES/WARNINGS/ADVISORIES... SMALL CRAFT ADVISORY UNTIL 6 PM HST THIS EVENING FOR ALENUIHAHA CHANNEL. && $$ RYSHKO