541
FXHW60 PHFO 050140
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
340 PM HST WED NOV 4 2009
SYNOPSIS
MODERATE TO FRESH TRADE WINDS WILL CONTINUE INTO THE WEEKEND...
BEFORE POSSIBLY VEERING TO THE SOUTHEAST LATE THIS WEEKEND. A
SHOWERY CLOUD BAND WILL CONTINUE TO MOVE DOWN THE ISLAND CHAIN...
GRADUALLY CLEARING KAUAI AND OAHU OVERNIGHT. THE CLOUD BAND WILL
CLEAR MAUI COUNTY AND THE BIG ISLAND THURSDAY MORNING...AND A
RELATIVELY DRY TRADE WIND PATTERN WILL PREVAIL INTO THE
WEEKEND...WITH JUST A FEW PASSING WINDWARD SHOWERS.
DISCUSSION
VISIBLE SATELLITE IMAGERY HIGHLIGHTS A SOUTHWARD MOVING SHOWERY
CLOUD BAND CURRENTLY AFFECTING KAUAI AND OAHU...AND ON THE DOORSTEP
OF THE ISLANDS IN MAUI COUNTY. THIS 125 MILE WIDE...E-W ORIENTED...
BAND OF BROKEN TO OVERCAST SHOWERY LOW CLOUDS IS SAGGING SOUTHWARD
NEAR 10 MPH WITHIN A MODERATE TRADE WIND FLOW. GFS APPEARS TO BE
HANDLING THIS FEATURE FAIRLY WELL...AND IT/S SOLUTION SUGGESTING
THAT THIS BAND WILL MOVE S OVER THE ISLAND CHAIN THROUGH THURSDAY
MORNING...WHILE SLOWLY WEAKENING...IS DEEMED VALID. THE FORECAST
CALLS FOR THE MOISTURE ASSOCIATED WITH THIS BAND TO CLEAR KAUAI THIS
EVENING...OAHU AROUND MIDNIGHT...BUT LINGERING OVER WINDWARD MAUI
AND BIG ISLAND INTO THURSDAY MORNING. ALTHOUGH THE BULK OF THIS
LOW-TOPPED MOISTURE /1O KFT CLOUD TOPS/ WILL AFFECT WINDWARD
SLOPES AND SHORES...SOME CLOUDS AND SHOWERS WILL SPREAD LEEWARD.
ON THE LARGER SCALE...NEARLY STATIONARY HIGH PRESSURE CENTERED ABOUT
1300 MILES NW OF KAUAI CONTINUES TO GRADUALLY WEAKEN...WHILE AN
INTENSE LOW ALOFT IS NOW ABOUT 950 MILES W OF KAUAI...AND MOVING W.
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. 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.
AS WE LOOK TOWARD NEXT WEEK...THE LONGER TERM FORECAST REMAINS A
CHALLENGE. GLOBAL MODELS CONTINUE TO OFFER DRAMATICALLY DIFFERENT
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
A SMALL CRAFT ADVISORY /SCA/ IS IN EFFECT FOR THE TYPICALLY
WINDIER WATERS N AND S OF THE BIG ISLAND...AND FOR WATERS N AND W OF
KAUAI...WHERE THIS MORNING/S QUIKSCAT PASS SHOWED 25 KT. SOME
MODERATION OF THE TRADE FLOW IS EXPECTED ON THURSDAY...AND HAVE
ELECTED TO KEEP THE CURRENT EXPIRATION TIME OF 6 AM THURSDAY...
IN HOPES THAT TONIGHT/S QUIKSCAT PASS PROVIDES ADDITIONAL INSIGHT.
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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