FXHW60 PHFO 290551
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST SAT NOV 28 2009
.SYNOPSIS...
TRADE WINDS AND WINDWARD SHOWERS BOTH WILL INCREASE TONIGHT INTO
SUNDAY...AND A COLD LOW IN THE MIDDLE ATMOSPHERE WILL SPREAD HEAVIER
SHOWERS AND POSSIBLY THUNDERSTORMS ACROSS THE STATE FROM SUNDAY INTO
MONDAY. MORE TYPICAL TRADE-WIND CONDITIONS WILL RETURN BY
WEDNESDAY...FOLLOWED BY LIGHT SOUTHEASTERLY WINDS AROUND THURSDAY.
A COLD FRONT MAY REACH THE STATE NEXT FRIDAY OR SATURDAY.
&&
.DISCUSSION...
TRADE-WIND SHOWERS UPWIND OF THE MAIN HAWAIIAN ISLANDS ALREADY
SHOWED MORE VERTICAL DEVELOPMENT THAN USUAL...THOUGH THEY REMAINED
LARGELY UNORGANIZED. THE FRONT TO THE NORTH WITHERED AS IT TRIED TO
PUSH THROUGH THE STUBBORN SUBTROPICAL RIDGE. TIME WILL TELL HOW MUCH
OF THE VORTICITY AND MOISTURE ASSOCIATED WITH THE FRONT WILL SURVIVE
THE TRIP SOUTH. SURFACE DATA AROUND THE STATE REPORTED ONLY MODERATE
TRADE WINDS...BUT PRESSURE TRENDS POINTED TOWARD A GRADUAL INCREASE
IN GRADIENT. THIS TREND LIKELY WILL ACCELERATE...REBUILDING THE
SUBTROPICAL RIDGE VERY QUICKLY BEHIND THE FRONT FROM TONIGHT INTO
SUNDAY...BRINGING THE TRADES BACK UP AGAIN FROM SUNDAY MORNING INTO
MONDAY MORNING.
A SOLID MODEL CONSENSUS STILL SUGGESTS THAT THE NEXT MID-LEVEL
TROUGH WILL START TO DEEPEN OVER THE ISLANDS AS EARLY AS SUNDAY
MORNING...AND PROBABLY WILL CUT OFF INTO A LOW WITH AN IMPRESSIVE
COLD POOL. GUIDANCE STILL DIFFERS WITH RESPECT TO THE SOUTHWESTWARD
PROGRESS AND INTENSITY OF THIS COLD POOL...BUT RECENT RUNS HAVE BEEN
MOVING CLOSER TOGETHER IN FAVORING A SLIGHTLY SLOWER DEVELOPMENT. AT
A MINIMUM...THE LOW WILL PROVIDE INCREASED UPPER SUPPORT FOR SHOWER
GROWTH. IF THE COLD POOL PROVES TO BE AS DEEP AS SOME SOLUTIONS
SUGGEST...THEN THUNDERSTORM DEVELOPMENT COULD BE GENUINELY
WIDESPREAD. HOWEVER...A MORE MODERATE OUTCOME SEEMS MORE LIKELY...
AND THE CURRENT FORECAST APPEARS TO BE OVERDONE A BIT. STILL...AT
THIS POINT IT WOULD NOT BE PRUDENT TO YO-YO THE FORECAST UNLESS
STRONGER DISSENTING EVIDENCE BECOMES AVAILABLE.
THUS...THE WHOLE SCENARIO MAY END UP LOOKING LIKE A REPEAT OF
EARLIER THIS WEEK...WITH MODERATE TO STRONG TRADES...LOCALLY HEAVY
TRADE-WIND SHOWERS...AND THE POTENTIAL FOR CONSIDERABLE THUNDER. THE
FRONT ITSELF IS NOT EXPECTED TO SURVIVE ITS PASSAGE THROUGH THE
RIDGE...BUT ITS REMNANTS WILL TRAVEL FAR ENOUGH SOUTHEAST TO FEED
THE CONVECTION OVER THE STATE ANYWAY. IT REMAINS TO BE SEEN WHETHER
MODEL PREDICTIONS OF A MOISTURE PLUME FROM THE DEEP TROPICS REACHING
THE STATE DURING THIS SAME TIME WILL MATERIALIZE...BUT IF THEY
PROVE CORRECT...THEN THE CHANCES FOR HEAVY RAIN WILL INCREASE
FURTHER.
THE MORE EXTREME WEATHER PROBABLY WILL WIND DOWN BY WEDNESDAY AS THE
MID-LEVEL LOW LIFTS OUT AGAIN...AND HIGH PRESSURE REESTABLISHES
ITSELF ALOFT. MODERATE TRADES ARE EXPECTED TO RETURN BY THE MIDDLE
OF NEXT WEEK WITH MORE TYPICAL TRADE-WIND SHOWERS...ONLY TO BE
REPLACED AGAIN BY WEAK SOUTHERLIES AHEAD OF AN OSTENSIBLY STRONGER
FRONT APPROACHING THE STATE BY NEXT WEEKEND.
&&
.MARINE...
THE HIGH SURF ADVISORY FOR EAST-FACING SHORES IS STILL SET TO EXPIRE
SUNDAY MORNING AT 6 AM HST...AND WITH REPORTS TRENDING DOWN IT MAY
BE CANCELLED EARLIER. SURF ALONG NORTH-FACING SHORES WILL REMAIN
LARGER THAN USUAL...BUT IS NOT EXPECTED TO EXCEED THE ADVISORY
LEVEL THROUGH MID WEEK. SOUTH-FACING SHORES WILL SEE SOME SMALL
SOUTHERN SWELL THIS WEEK AS WELL.
BUILDING WINDS AND LOCALLY GENERATED SEAS ONCE AGAIN REQUIRE A SMALL
CRAFT ADVISORY FOR THE USUAL WINDY ZONES TONIGHT...AND THE AFFECTED
AREA MAY EXPAND LATER IN THE WEEKEND AS WIND SPEED RISES.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST SUNDAY FOR NIIHAU-KAUAI
WINDWARD-OAHU KOOLAU-OLOMANA-MOLOKAI-MAUI WINDWARD WEST-WINDWARD
HALEAKALA-BIG ISLAND NORTH AND EAST.
SMALL CRAFT ADVISORY UNTIL 6 AM HST MONDAY FOR KAUAI NORTHWEST
WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-KAUAI CHANNEL-
OAHU WINDWARD WATERS-OAHU LEEWARD WATERS-KAIWI CHANNEL-
ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG ISLAND
SOUTHEAST WATERS.
&&
$$
RYSHKO
