FXHW60 PHFO 151330
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST TUE DEC 15 2009
.SYNOPSIS...
HIGH PRESSURE NORTH OF THE ISLANDS WILL KEEP THE ISLANDS RELATIVELY
DRY THROUGH WEDNESDAY. A COLD FRONT WILL MOVE DOWN THE ISLAND CHAIN
LATE WEDNESDAY THROUGH EARLY FRIDAY...BRINGING SHOWERS WITH IT. HIGH
PRESSURE BEHIND THE FRONT...WILL BRING BACK MODERATE TRADE WINDS
THIS WEEKEND.
&&
.DISCUSSION...
THE WEAK COLD FRONT NORTHWEST OF KAUAI BEGAN TO SHOW SIGNS OF
LIFTING TO THE NORTH JUST AFTER MIDNIGHT. THIS FRONT IS ASSOCIATED
WITH A LOW PRESSURE SYSTEM FAR NORTH-NORTHEAST OF THE ISLANDS WHICH
CONTINUES TO MOVE TO THE EAST. A FEW CLOUDS DID FORM OVER KAUAI
OVERNIGHT...AND BROUGHT ISOLATED SHOWERS TO THE GARDEN ISLE. A FEW
SHOWERS ALSO FORMED OVER OAHU. THE CLOUDS OVER OAHU WERE LIFTING
NORTH AND SHOULD DISSIPATE WELL BEFORE SUNRISE.
THE NEXT MAJOR WEATHER FEATURE IS THE FRONT ASSOCIATED WITH A LOW
THAT IS CURRENTLY MORE THAN 1500 MILES NORTH-NORTHWEST OF KAUAI.
THIS FRONT IS EXPECTED TO REACH KAUAI WEDNESDAY OR WEDNESDAY NIGHT.
THERE REMAINS GOOD MODEL AGREEMENT WITH THE HANDLING OF THIS SYSTEM
THROUGH THE WEEK. THE LOW WILL MOVE TO THE EAST OVER THE NEXT 24
HOURS...AND THEN START TO TAKE A LITTLE BIT OF A NORTHEAST TURN. THE
FRONT WILL BE MOVING DOWN THE NORTHWESTERN ISLAND CHAIN...AND SHOULD
MAKE IT TO KAUAI LATE WEDNESDAY. AS THE FRONT MAKES IT TO KAUAI...IT
LOOKS LIKE ITS FORWARD MOMENTUM WILL SLOW...BRINGING IT TO MAUI BY
FRIDAY BEFORE DISSIPATING.
ALL THE MODELS SHOW AT LEAST A BROAD DEEPENING UPPER LOW JUST WEST
OF THE SURFACE FEATURE. THE ECMWF IS THE FIRST TO CUT OFF AN UPPER
LEVEL LOW ALONG THE TROUGH...BUT THE GFS FOLLOWS SUIT 12 HOURS
LATER. THE NAM AND UKMET DO NOT CUT OFF A LOW.
THE UPPER TROUGH WILL HELP TO ENHANCE SHOWER ACTIVITY WITH THE
FRONT. 500 MB TEMPERATURES...NORMALLY AROUND -8 DEGREES CELSIUS THIS
TIME OF YEAR...ARE FORECAST TO DROP TO -12 THURSDAY. GUIDANCE SHOWS
ABOUT A 30 PERCENT CHANCE FOR THUNDERSTORMS LATE WEDNESDAY NIGHT AND
INTO THURSDAY. THE GFS BACKED OFF A BIT ON THE THUNDERSTORM CHANCES
THIS LATEST CYCLE...SO HAVE GONE BACK AND FORTH ABOUT ADDING THEM
INTO THE FORECAST...BUT ULTIMATELY HAVE DECIDED TO ONCE AGAIN HOLD
OFF.
ALTHOUGH SURFACE WINDS ARE NOT EXPECTED TO BE STRONG WITH THIS NEXT
FRONT...THE WINDS AT THE UPPER ELEVATIONS MAY STILL REACH ADVISORY
LEVELS.
MODERATE TRADES ARE EXPECTED TO MAKE A SOMEWHAT BRIEF RETURN THIS
WEEKEND. AS WE HEAD INTO THE START OF THE NEW WEEK...THE HIGH
PRESSURE RIDGE WILL SINK SOUTHWARD...WEAKENING THE TRADE WIND FLOW.
&&
.MARINE...
SURF FROM A NORTHWEST SWELL IS NOT EXPECTED TO REACH ADVISORY LEVEL
TUESDAY.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
