028
FXHW60 PHFO 042325
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
125 PM HST WED NOV 4 2009
UPDATE
HAVE UPDATED GRIDS AND CORRESPONDING PUBLIC FORECASTS TO ACCOUNT FOR
CURRENT SATELLITE OBSERVATIONS. A SHOWERY CLOUD BAND HAS ARRIVED
OVER KAUAI AND OAHU...AND IS STILL EXPECTED TO MOVE OVER MAUI
COUNTY THIS AFTERNOON. THE BIG ISLAND WILL REMAIN MOSTLY DRY THROUGH
THE DAY...AS THE CLOUD BAND IS NOT EXPECTED TO ARRIVE OVER WINDWARD
BIG ISLAND UNTIL AFTER DARK. THUS HAVE LOWERED SKY AND POP AMOUNTS
FOR WINDWARD BIG ISLAND...AND HAVE CLEANED UP WORDING IN SOME OF THE
OTHER PRODUCTS.
SYNOPSIS
MODERATE TO FRESH TRADE WINDS WILL CONTINUE INTO THE WEEKEND...
BEFORE POSSIBLY VEERING TO THE SOUTHEAST LATE THIS WEEKEND. A
SHOWERY CLOUD BAND IS APPROACHING THE ISLANDS FROM THE NORTHEAST...
AND WILL BRING ANOTHER ROUND OF SHOWERS TO KAUAI LATER THIS MORNING
AND AFTERNOON. THE BAND WILL MOVE OVER OAHU BY THIS AFTERNOON AS
WELL...EXTENDING TO MAUI COUNTY AND THE BIG ISLAND BY THIS EVENING.
THE TRADES WILL CONTINUE TO BRING A FEW PASSING WINDWARD SHOWERS
INTO THE WEEKEND.
DISCUSSION
INITIAL VISIBLE IMAGES OF THE DAY SHOW A PEPPERING OF TRADE CUMULUS
ALONG WINDWARD SLOPES AND SHORES THIS MORNING...WITH FEW LOW CLOUDS
OVER LEEWARD AREAS. THE LEADING EDGE OF A 125 MILE WIDE...E-W
ORIENTED...BAND OF BROKEN TO OVERCAST SHOWERY LOW CLOUDS IS JUST NE
OF KAUAI THIS MORNING...AND IS SAGGING SOUTHWARD WITHIN THE MODERATE
TRADE WIND FLOW. THE BAND HAS BEEN MOVING SSW AT 10 TO 15 MPH...
WHILE CLOUD ELEMENTS WITHIN THE BAND ARE MOVING TOWARD THE WSW. GFS
HAS SHOWN RUN-TO-RUN CONSISTENCY WITH THIS FEATURE...AND HAS
INITIALIZED WELL THIS MORNING. THUS IT/S SOLUTION SUGGESTING THAT
THIS BAND WILL MOVE S OVER THE ISLAND CHAIN THROUGH TONIGHT...WHILE
SLOWLY WEAKENING...IS DEEMED VALID. ROUGH ESTIMATE ON TIMING IS
KAUAI LATER THIS MORNING...OAHU AROUND MID-DAY...MAUI COUNTY EARLY
THIS EVENING...AND BIG ISLAND TONIGHT. ALTHOUGH THE BULK OF THIS
LOW-TOPPED MOISTURE /1O-15 KFT CLOUD TOPS/ WILL AFFECT WINDWARD
SLOPES AND SHORES...SOME CLOUDS AND SHOWERS WILL SPREAD LEEWARD.
ONCE IT ARRIVES...EXPECT 8 TO 12 HOURS BEFORE THE BAND CLEARS AN
ISLAND.
ON THE LARGER SCALE...NEARLY STATIONARY HIGH PRESSURE CENTERED ABOUT
1300 MILES NW OF KAUAI HAS WEAKENED OVER THE PAST 24 HOURS...WHILE A
LOW ALOFT NOW ABOUT 800 MILES W OF KAUAI HAS INTENSIFIED WHILE
MOVING BRISKLY TOWARD THE W. THE DEPARTURE OF THE LOW HAS CLEARED
ISLAND SKIES OF MOST OF YESTERDAY/S HIGH CLOUDS...AND ALLOWED A
STABILIZING INVERSION NEAR 10 KFT TO APPEAR IN THE EARLY MORNING
PHLI SOUNDING...WHILE THE PHTO INVERSION IS LOWER...NEAR 7 KFT.
THE FORECAST CALLS FOR THE LOW ALOFT TO GRADUALLY FILL AS IT MOVES
FURTHER AWAY TO THE W...ALLOWING A MID-LEVEL RIDGE TO BUILD OVER THE
ISLANDS FROM THE NW. THIS RIDGE ALOFT WILL BE SITUATED OVER THE
ISLANDS FROM THURSDAY THROUGH THE WEEKEND...BEFORE BREAKING DOWN
EARLY NEXT WEEK. THE PRESENCE OF THE RIDGE WILL ENSURE A STABLE
ISLAND ATMOSPHERE. AT THE SURFACE...THE CURRENT FORECAST CALLS FOR
THE HIGH TO THE NW TO WEAKEN IN PLACE WHILE A NEW HIGH MOVES IN JUST
N OF THE OLD ONE OVER THE NEXT DAY OR SO. THIS NEW HIGH WILL TRACK
STEADILY E WELL TO THE N OF THE ISLANDS THROUGH THE WEEKEND...
THEREBY SUPPORTING WHAT APPEARS TO BE A MODERATE TRADE WIND FLOW.
THIS COMBINATION IS EXPECTED TO LEAD TO A FAIRLY QUIET TRADE WIND
PATTERN IN THE WAKE OF TODAY AND TONIGHT/S SHOWER BAND. AS THE HIGH
DISTANCES ITSELF TO THE NE LATE THIS WEEKEND...THE TRADE FLOW OVER
THE ISLANDS IS EXPECTED TO VEER TO THE SE.
THE LONGER TERM FORECAST...FINISHING OUT THE WEEKEND AND INTO NEXT
WEEK...REMAINS A CHALLENGE. GLOBAL MODELS ARE OFFERING DRAMATICALLY
DIFFERING SOLUTIONS FROM ONE ANOTHER...AND WITH THE GFS SHOWING
ESSENTIALLY NO RUN-TO-RUN CONSISTENCY...WE HAVE LITTLE CONFIDENCE IN
FORECAST DETAILS AS WE HEAD INTO NEXT WEEK.
MARINE
THE SMALL CRAFT ADVISORY /SCA/ IS NOW IN EFFECT FOR THE TYPICALLY
WINDIER FOR WATERS N AND S OF THE BIG ISLAND...AND THIS MORNING/S
QUIKSCAT PASS DETECTED 25 KT IN THE ALENUIHAHA CHANNEL...AND OVER
WATERS N AND W OF KAUAI. WILL BE EXTENDING THE SCA TO INCLUDE THESE
KAUAI WATERS...AND WILL EXTEND THE SCA THROUGH TONIGHT FOR ALL THE
INCLUDED ZONES.
HFO WATCHES/WARNINGS/ADVISORIES
SMALL CRAFT ADVISORY UNTIL 6 AM HST THURSDAY FOR KAUAI NORTHWEST
WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-ALENUIHAHA
CHANNEL-BIG ISLAND SOUTHEAST WATERS.
BIRCHARD
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