904
FXHW60 PHFO 040604
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
800 PM HST TUE NOV 3 2009
SYNOPSIS
A DEVELOPING TROUGH WEST OF KAUAI WILL FOCUS SHOWERS OVER WINDWARD
PORTIONS OF KAUAI AND OAHU THROUGH TONIGHT...BEFORE DIMINISHING ON
WEDNESDAY AS THE TROUGH MOVES FURTHER AWAY TO THE WEST. OTHERWISE...
WE CAN EXPECT BREEZY TRADE WINDS TO CONTINUE THROUGH MOST OF THE
WORK WEEK...WITH WINDS DIMINISHING AND BECOMING SOUTHEASTERLY OVER
THE WEEKEND. THE BREEZY TRADES WILL DELIVER A FEW PASSING WINDWARD
SHOWERS...BUT THEIR INTENSITY AND COVERAGE WILL BE LIMITED AS THE
ISLAND ATMOSPHERE WILL BE STABLE FROM WEDNESDAY INTO THE WEEKEND.
DISCUSSION
THE FORECAST IS LOOKING OK TO START THE MID SHIFT. REGARDLESS OF
ANY MINOR TWEAKS...IT LOOKS LIKE A PRETTY SHOWERY NIGHT IS IN STORE
FOR MOST OF THE STATE...WITH THE BIG ISLAND STAYING THE DRIEST OF
THE ISLANDS.
NOT ANTICIPATING ANY BIG CHANGES TO THE FORECAST TONIGHT. DEEP
LAYERED TROUGHING OVER THE EASTERN NORTH PACIFIC WILL KEEP HIGH
PRESSURE NEARLY STATIONARY TO OUR NORTHWEST WITH ITS ATTENDANT RIDGE
NORTHEAST OF HAWAII. THE INFRARED SATELLITE IMAGERY CLEARLY DEPICTS
MID LEVEL CYCLOGENESIS JUST WEST OF THE STATE AT THIS TIME. AS OF
NOW...GLOBAL SOLUTIONS ONLY DEVELOP A WEAK SURFACE REFLECTION AS THE
UPPER LOW DRIFTS SLOWLY WESTWARD WHILE UNDERCUTTING THE DEEP LAYERED
HIGH TO THE NORTH. AS THE LOW CONTINUES TO TRACK WEST...EXPECT
RISING 500 MB HEIGHTS LOCALLY WHICH WILL STRENGTHEN THE LOW LEVEL
SUBSIDENCE INVERSION AGAIN LIMITING THE VERTICAL DEVELOPMENT OF ANY
SHOWERS. SHOWER ACTIVITY WILL BECOME EVEN MORE FOCUSED ON WINDWARD
ZONES ALLOWING LEEWARD SECTIONS TO DRY OUT SOME COMPARED TO TODAY
AND MONDAY.
EXPECT TRADES FOR THE REMAINDER OF THE WORK WEEK WITH INTERMITTENT
PERIODS OF MORE PERSISTENT RAINFALL AS BANDS OF REMNANT FRONTAL
MOISTURE PASS OVER THE AREA. DURING THE REMAINDER WEEK...
PRESSURES/HEIGHTS WILL RISE OVER THE FAR EASTERN NORTH PACIFIC AS
THE POLAR JET FLATTENS. THIS WILL ALLOW HIGH PRESSURE TO OUR
NORTH TO SLIDE EASTWARD. ALONG WITH THE AFOREMENTIONED UPPER LOW AND
ITS ASSOCIATED INVERTED SURFACE TROUGH...THIS WILL CAUSE TRADE WINDS
TO BEGIN VEERING TO THE SOUTHEAST OVER THE WEEKEND. THE GFS AND
ECMWF...ALONG WITH GFS ENSEMBLES SUGGEST HEIGHT FALLS OVER THE
CENTRAL NORTH PACIFIC DUE TO A DEVELOPING SOUTHERN STREAM
SHORTWAVE...ALTHOUGH GUIDANCE STILL HAS TO RESOLVE MODERATE
DIFFERENCES REGARDING INTENSITY AND SURFACE FEATURES. CONFIDENCE IN
SOUTHEASTERLY FLOW ACROSS THE STATE OVER THE WEEKEND INTO EARLY NEXT
WEEK IS FAIR. IT IS FAR TOO EARLY TO DETERMINE ANY FRONTAL IMPACTS
DURING THE FIRST HALF OF NEXT WEEK THOUGH. WILL REVISIT THIS TONIGHT
FOR THE ADDITION OF DAY 7 TO THE GRIDS.
PREVIOUS DISCUSSION
/ISSUED 330 PM HST TUESDAY/
THE CURRENT FORECAST CONTINUES TO REFLECT A RATHER DRAMATIC
DEPARTURE FROM WHAT HAD BEEN ADVERTISED OVER THE PAST COUPLE OF
DAYS...AS A FRONTAL BOUNDARY NW OF KAUAI IS NO LONGER EXPECTED TO
MOVE DOWN THE ISLAND CHAIN...BRINGING A SIGNIFICANTLY COOLER/DRIER
AIR MASS TO THE ISLANDS. INSTEAD...THE ISLANDS WILL REMAIN TO THE S
OF THIS BOUNDARY...AND THUS DEW POINTS WILL REMAIN IN THE UPPER
60/S...WITH LITTLE CHANGE TO THE CURRENT AIR MASS.
THE FORECAST NOW CALLS FOR A DEVELOPING SURFACE WAVE ALONG THE
NEARBY FRONTAL BOUNDARY TO TRACK W...IN CONJUNCTION WITH IT/S MID-
AND UPPER-LEVEL SUPPORT...WHICH IS CLEARLY DEFINED IN WATER VAPOR
IMAGERY AS A DEVELOPING CUT-OFF LOW ALOFT NEAR 24N 165W. AS THIS
SURFACE TROUGH SHARPENS JUST W OF KAUAI THROUGH TONIGHT...TRADE
WINDS WILL BE STRONGER OVER THE NW PORTION OF THE ISLAND CHAIN...AND
THE ASSOCIATED TIGHTENING OF THE SURFACE GRADIENT WILL SUPPORT
LOW-LEVEL CONVERGENCE...AND SHOWER DEVELOPMENT...IN THE SAME GENERAL
AREA.
AS THE LOW ALOFT PROGRESSIVELY TRACKS W OVER THE NEXT SEVERAL
DAYS...IT/S INDUCED SURFACE TROUGH WILL FOLLOW SUIT...AND STRONG
TRADE WINDS NEAR KAUAI WILL DIMINISH SOMEWHAT ON WEDNESDAY.
MEANWHILE...A STRONG SURFACE HIGH FAR TO THE NW WILL WEAKEN WHILE
REMAINING STATIONARY INTO WEDNESDAY NIGHT...AND WILL THEN BUILD E
WELL N OF THE ISLANDS. THIS WILL SUPPORT A MODERATE TO FRESH TRADE
WIND FLOW OVER THE ISLANDS INTO THE WEEKEND. WITH AN UPPER RIDGE
FORECAST TO DEVELOP OVER THE ISLANDS LATER WEDNESDAY...AND INTO THE
WEEKEND...TRADE WIND SHOWERS WILL BE LIMITED IN THEIR COVERAGE AND
INTENSITY. THE HIGH WILL CONTINUE TO TRACK E OVER THE WEEKEND...AND
WINDS OVER THE ISLANDS WILL VEER TO THE SE. THE SURFACE RIDGE MAY
MOVE OVER THE ISLANDS ON MONDAY AND TUESDAY IN ADVANCE OF AN
APPROACHING FRONT.
MARINE
THE OAHU SURF FORECAST /SRFHFO/ CONTAINS A DETAILED LOOK AT EXPECTED
SURF AND SWELL CONDITIONS OVER THE NEXT COUPLE OF DAYS...AND CAN BE
LOOSELY APPLIED TO THE OTHER MARINE AREAS. A SMALL CRAFT ADVISORY
/SCA/ IS CURRENTLY IN EFFECT FOR MOST WATERS AROUND KAUAI AND
OAHU...WITH COMBINED SEAS AT OR ABOVE 10 FEET. STRONG N/NE WINDS
JUST NW OF THE FRONTAL BOUNDARY NW OF KAUAI ARE RESPONSIBLE FOR THE
ELEVATED SEAS...AND SURF OBSERVATIONS FROM NORTH SHORE KAUAI THIS
MORNING INDICATED SURF ABOVE ADVISORY LEVELS. THUS...A HIGH SURF
ADVISORY /HSA/ WAS ISSUED FOR NORTH FACING SHORES OF KAUAI COUNTY
THIS MORNING. SEAS ARE ALREADY DROPPING AT BUOY 51001 AND THE SURF
IS EXPECTED TO DROP BELOW ADVISORY LEVELS EARLY WEDNESDAY. WILL KEEP
AN EYE ON BUOY OBSERVATIONS TONIGHT. STILL ANTICIPATING ALLOWING THE
HIGH SURF ADVISORY TO EXPIRE AT 400 AM HST WEDNESDAY MORNING.
AVIATION
MOST OF THE TERMINAL SHOULD REMAIN PREDOMINANTLY VFR OVERNIGHT WITH
MAYBE A PASSING SHOWER THAT LOWERS CIGS/VIS TO MVFR. WITH THE
WIDESPREAD SHOWER ACTIVITY...WINDWARD TERRAIN OF THE SMALLER ISLANDS
SHOULD SEE MAINLY MVFR CIGS/VIS OVERNIGHT.
TRADE WINDS ARE CREATING SOME LOW LEVEL TURB LEE OF THE MOUNTAINS.
THIS WILL LIKELY PERSIST AS LONG AS THE TRADES DO.
ADDITIONALLY...STRONG DIFFLUENCE DOWNSTREAM FROM AN 80-90 KT JET MAX
IS CREATING SOME MODERATE HIGH LEVEL TURBULENCE BETWEEN FL250/FL350.
THIS IS ALSO EXPECTED TO CONTINUE BEYOND 04/12Z.
HFO WATCHES/WARNINGS/ADVISORIES
HIGH SURF ADVISORY UNTIL 4 AM HST WEDNESDAY FOR NIIHAU-KAUAI
WINDWARD-KAUAI LEEWARD.
SMALL CRAFT ADVISORY UNTIL 6 PM HST WEDNESDAY FOR KAUAI
NORTHWEST WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-
KAUAI CHANNEL-OAHU WINDWARD WATERS.
PUBLIC/AVIATION...DEJESUS
MARINE...BIRCHARD/DEJESUS
PREVIOUS...BIRCHARD
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