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Hawaiian Islands Synoptic Discussion and Guidance
975
FXHW60 PHFO 211342
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
342 AM HST SAT NOV 21 2009
.SYNOPSIS...
TRADE WINDS WILL CONTINUE THROUGH THE WEEKEND AS HIGH PRESSURE
REMAINS FAR NORTH OF THE ISLANDS. SHOWERS WILL FOCUS ON WINDWARD
AND MOUNTAIN SLOPES...WITH A FEW SHOWERS REACHING LEEWARD
LOCATIONS. TRADES WILL WEAKEN SLIGHTLY EARLY NEXT WEEK.
&&
.DISCUSSION...
RAINFALL CONTINUES SPARSE OVERNIGHT WITH THE HAWAII RAIN GAGE
NETWORK ONLY SHOWING LIGHT RAINFALL OVER THE WINDWARD BIG
ISLAND. GAGES ALONG THE NORTHEAST LOWER SLOPES OF THE BIG ISLAND
RANGED FROM ZERO TO A QUARTER OF AN INCH WHILE WINDWARD GAGES ON
THE SMALLER ISLANDS DID NOT SEE ANY RAINFALL. THE DRY WEATHER IS
EXPECTED TO CONTINUE TODAY...AND THE POP GRIDS REFLECT
THIS...REPRESENTING A DRY TRADE WEATHER REGIME OF SCATTERED
SHOWERS AND CLOUDY SKIES OVER WINDWARD AREAS...WITH MOSTLY CLEAR
SKIES AND A SMALL CHANCE OF SHOWERS OVER LEEWARD LOCATIONS.
THE OVERNIGHT SOUNDINGS FROM LIHUE AND HILO ARE SIMILAR TO FRIDAY
AFTERNOONS/ SHOWING A DRY ATMOSPHERE WITH PRECIPITABLE WATER
VALUES NEAR ONE INCH...WHICH IS IN STARK CONTRAST TO THE TWO INCH
PW VALUES DURING LAST WEEKEND/S FLOOD EVENT. PW VALUES ARE
EXPECTED TO SLOWLY INCREASE OVER THE WEEKEND...AND INTO NEXT
WEEK...BRINGING A MORE CLIMATOLOGICAL TRADE WIND WEATHER PATTERN
...WITH SHOWERS INCREASING OVER WINDWARD LOCATIONS.
A 1027 MB HIGH PRESSURE FAR NORTH OF THE STATE IS MAINTAINING THE
FRESH TO STRONG TRADE WINDS ACROSS THE ISLANDS. STORM SYSTEMS
RACING ACROSS THE NORTH PACIFIC ARE FORECAST TO PUSH THE HIGH
TOWARD THE EAST AND ITS ASSOCIATED SURFACE RIDGE SOUTH OVER THE
WEEKEND AND NEXT WEEK... THEREBY RELAXING THE PRESSURE GRADIENT
OVER THE STATE AND DECREASING THE TRADE WINDS INTO THE MODERATE TO
FRESH RANGE EARLY NEXT WEEK.
THE GFS AND ECMWF BOTH SHOW A WEAK COLD FRONT APPROACHING KAUAI
TUESDAY NIGHT AND WEDNESDAY...BUT NEVER REACHING THE GARDEN ISLE.
THE MODELS DO SHOW TROPICAL MOISTURE BEING DRAWN UP FROM THE SOUTH
IN RESPONSE TO THE FRONT...INCREASING PW VALUES NEAR THE BIG
ISLAND TUESDAY NIGHT...AND THEN MAUI COUNTY AND OAHU ON WEDNESDAY.
THIS SCENARIO WOULD BRING INCREASING SHOWERS TO WINDWARD AREAS OF
THOSE ISLANDS. HOWEVER...PREVIOUS MODEL RUNS HAD SHOWN A SURFACE
TROUGH OR EVEN A WEAK SURFACE LOW ACCOMPANYING THIS MOISTURE...SO
THE MODELS HAVE BEEN TRENDING TOWARD A WEAKER FEATURE OVER THE
PAST FEW DAYS. THE WEAKENING TREND DOES NOT BODE MUCH CONFIDENCE
IN THIS FEATURE...SO THE FORECAST REMAINS WITH CLIMO TRADE WIND
WEATHER.
&&
.MARINE...
A LARGE NORTHWEST SWELL IS EXPECTED TO BEGIN FILLING IN SATURDAY
NIGHT...LIKELY REACHING ADVISORY LEVELS SUNDAY AND MONDAY THEN
SLOWLY LOWERING INTO TUESDAY. A LARGER NORTHWEST SWELL IS EXPECTED
TO FILL IN TUESDAY NIGHT...AND PEAK LATE WEDNESDAY OR WEDNESDAY
NIGHT.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 5 PM HST SUNDAY FOR KAUAI CHANNEL-
KAIWI CHANNEL-MAALAEA BAY-PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG
ISLAND LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS.
&&
$$
MORRISON
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office
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This page is maintained voluntarily by the MKWC and the UHMET faculty, staff, and students.
It was last modified on: Tue, Jun 16 2009 - 0632 UTC
Send comments to: Ryan Lyman
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