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Hawaiian Islands Synoptic Discussion and Guidance

119
FXHW60 PHFO 011416
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST SUN FEB 1 2015

.SYNOPSIS...
LIGHT TO MODERATE TRADES WILL CONTINUE THROUGH TONIGHT AS WEAK
SURFACE HIGH PRESSURE REMAINS TO THE NORTH OF THE MAIN HAWAIIAN
ISLANDS. WINDS WILL BEGIN TURNING TO THE SOUTHWEST AND BECOMING
WINDY LATE MONDAY AND INTO TUESDAY AS A FRONT REACHES THE AREA.
ADDITIONAL FRONTS MAY IMPACT THE ISLANDS...KEEPING PREVAILING STRONG
WEST TO NORTHWEST WINDS DURING MOST OF THE WORK WEEK. SHOWERS WILL
FAVOR WINDWARD AND MAUKA AREAS TODAY...THEN SPREADING INTO LEEWARD
AREAS AS THE VARIOUS FRONTS REACH THE ISLANDS DURING THE NEXT
SEVERAL DAYS.

&&

.DISCUSSION...
WEAK HIGH PRESSURE REMAINS TO THE N OF THE MAIN HAWAIIAN ISLANDS...
KEEPING A LIGHT TO MODERATE TRADE WIND PATTERN ACROSS THE AREA UNTIL
TONIGHT. AT 330 AM HST...MAUKA SHOWERS WERE STILL LINGERING OVER
WINDWARD MAUI...WITH LOCALIZED HEAVY RAIN AFFECTING LOCATIONS FROM
WAIHEE TO HONOKOHAU.

THE TRADES WILL PREVAIL UNTIL EARLY MON WHEN AN APPROACHING COLD
FRONT BOUNDARY FROM THE NW WILL VEER WINDS TO A MORE SW FLOW. LATEST
GLOBAL MODEL SOLUTIONS ARE SHOWING BETTER AGREEMENT IN BRINGING THE
LEADING EDGE OF THIS FRONT INTO THE NW PORTIONS OF THE ALOHA STATE
BY LATE MON NIGHT...AND MOVING DOWN THE ISLAND CHAIN THROUGH TUE.
SHOWERS WILL INCREASE WITH THE FROPA...WITH THE BULK OF THE RAIN
EXPECTED MON NIGHT AND TUE. ALSO...THE CONSENSUS BETWEEN ECMWF AND
GFS HAS IMPROVED IN THE LATEST RUNS WITH THE ECMWF SOLUTION STARTING
TO TREND TOWARDS A WETTER AND WINDIER SCENARIO. THEREFORE...THE
MORNING PACKAGE WILL CARRY STRONGER SW AND W WINDS MAINLY OVER THE
SMALLER ISLANDS WITH BREEZY CONDITIONS DEVELOPING ON MON
AFTERNOON/EVENING...THEN BECOMING WINDY MON NIGHT INTO TUE. THESE
STRONG SW WINDS MAY PRODUCE LOCALLY GUSTY DOWNSLOPE WINDS OVER NE
AND E FACING SLOPES OF SOME OF THE SMALLER ISLANDS...AND MAY
POSSIBLY CONTINUE THROUGH THU. RAINFALL IN GENERAL SHOULD REMAIN
IN THE MODERATE CATEGORY...BUT LOCALIZED HEAVY RAIN IS LIKELY.

MODELS ALSO SHOW TWO OTHER FRONTS MOVING JUST TO THE N OR ACROSS THE
AREA DURING THE SECOND HALF OF THE WEEK. TIMING STILL REMAINS
RATHER UNCERTAIN IN GUIDANCE...BUT IN GENERAL...EXPECT ANOTHER
FRONTAL SYSTEM APPROACHING OR REACHING THE AREA AROUND WED/WED
NIGHT...AND YET ANOTHER FRONT MOVING JUST TO THE N OF THE ISLAND
CHAIN IN THE LATE THU/EARLY FRI TIMEFRAME. SHOWER ACTIVITY WILL
INCREASE WITH EACH OF THESE SYSTEMS...WHICH WILL ALSO MAINTAIN THE
AFOREMENTIONED STRONG W FLOW ACROSS MAINLY THE SMALLER ISLANDS AND
ADJACENT WATERS. THIS TYPE OF FLOW IS VERY UNUSUAL ACROSS THE MAIN
HAWAIIAN ISLANDS FOR EXTENDED PERIODS OF TIME...WHICH MAY PRODUCE
LOCAL SURGES AND STRONG WIND GUSTS DUE TO DOWNSLOPE ACCELERATION.
TYPICAL AREAS THAT EXHIBIT THESE KIND OF ACCELERATED WINDS INCLUDE
THE NE AND E FACING SLOPES OF THE KOOLAU AND WAIANAE MOUNTAINS...
WHICH COULD BRING POTENTIAL FOR STRUCTURAL AND VEGETATION DAMAGE AS
WELL AS POWER OUTAGES. UPCOMING MODEL RUNS WILL PROVIDE A CLEARER
PICTURE OF WHAT TO EXPECT FOR THE WORK WEEK AHEAD...AND THE FORECAST
WILL BE ADJUSTED ACCORDINGLY.

MODELS FINALLY BRING BUILDING SFC HIGH PRESSURE OVER THE AREA BY
NEXT WEEKEND...BRINGING LIGHTER WINDS AND DRIER CONDITIONS.

&&

.AVIATION...
A WEAK RIDGE OF HIGH PRESSURE JUST NORTH OF THE ISLANDS WILL KEEP A
LIGHT WIND REGIME IN PLACE THROUGH TONIGHT...DOMINATED BY DAYTIME
SEA BREEZES AND OVERNIGHT LAND BREEZES. BEST CHANCES FOR MVFR CIGS
AND VSBYS IN SHRA WILL BE ACROSS WINDWARD AND MAUKA AREAS...WITH
GENERALLY VFR CONDITIONS ANTICIPATED ELSEWHERE.

AIRMETS REMAIN IN EFFECT FOR MTN OBSC OVER MOLOKAI...MAUI...AND THE
BIG ISLAND...AND THESE WILL LIKELY NEED TO BE EXTENDED BEYOND 16Z.
AIRMETS FOR MTN OBSC MAY BECOME NECESSARY ACROSS THE OTHER ISLANDS
THIS AFTERNOON.

&&

.MARINE...
THE HIGH SURF ADVISORY HAS BEEN EXTENDED THROUGH EARLY THIS EVENING
AS BUOY OBSERVATIONS DO NOT SHOW A CLEAR DOWNWARD TREND ON THIS
SWELL...WHICH CONTINUES TO PRODUCE COMBINED SEAS IN EXCESS OF 10 FT.
THEREFORE...THE SMALL CRAFT ADVISORY /SCA/ IS ALSO IN EFFECT
THROUGH EARLY THIS EVENING FOR AREAS EXPOSED TO THE SWELL.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST THIS EVENING FOR NORTH AND WEST
FACING SHORES OF NIIHAU AND KAUAI...AND FOR NORTH FACING SHORES OF
OAHU MOLOKAI AND MAUI.

SMALL CRAFT ADVISORY UNTIL 6 PM HST THIS EVENING FOR THE WATERS
SURROUNDING KAUAI...THE OAHU WINDWARD WATERS...THE KAIWI CHANNEL AND
THE MAUI COUNTY WINDWARD WATERS.

&&

$$

DISCUSSION/MARINE...REYNES
AVIATION...JELSEMA














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