Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 210632
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
832 PM HST SUN APR 20 2014

.SYNOPSIS...
STRONG HIGH PRESSURE TO THE NORTH OF THE STATE WILL CREATE LOCALLY
WINDY TRADES TONIGHT AND MONDAY. THE TRADES WILL EASE OFF A BIT AS
THE HIGH MOVES AWAY BY MIDWEEK. THE STRONG TRADES WILL CONTINUE TO
BLOW PASSING WINDWARD AND MAUKA SHOWERS OVER TO LEEWARD SIDES AT
TIMES THROUGH MONDAY OR MONDAY NIGHT. DRIER AIR AND FEWER SHOWERS
ARE EXPECTED FROM TUESDAY THROUGH THE REST OF THE WORK WEEK.

&&

.DISCUSSION...
RADAR LOOPS SHOW AN ACTIVE SHOWER PATTERN ACROSS WINDWARD PORTIONS
OF THE STATE DURING THE PAST SEVERAL HOURS...WITH SOME SHOWER
ACTIVITY SPILLING OVER INTO LEEWARD SECTIONS. RAIN GAUGES REPORT
MOSTLY LIGHT ACCUMULATIONS AS THE SHOWERS ARE MOVING QUICKLY
WITHIN RATHER BRISK TRADE WIND FLOW. THE 00Z SOUNDINGS SHOW WEAK
INVERSIONS BASED AROUND 7000 FEET...WITH AN OVERALL INCREASE IN
COLUMN MOISTURE DURING THE PREVIOUS 12 HOURS. PWATS HAVE INCREASED
TO AROUND THE 75TH PERCENTILE FOR THIS TIME OF YEAR. THIS IS
CONSISTENT WITH MIMIC-TPW SATELLITE IMAGERY...WHICH SHOWS AN AREA
OF RELATIVELY HIGHER MOISTURE MOVING WESTWARD THROUGH THE REGION.
AS HAS BEEN THE CASE FOR THE PAST COUPLE OF DAYS...ABUNDANT
MID/HIGH LEVEL CLOUDINESS CONTINUES TO STREAM NORTHWARD ACROSS THE
STATE...TO THE EAST OF A STATIONARY MID/UPPER LEVEL TROUGH
CENTERED SEVERAL HUNDRED MILES TO THE SOUTHWEST. AT THE
SURFACE...A 1032 MB HIGH IS NOW CENTERED ABOUT 1200 MILES DUE
NORTH OF THE BIG ISLAND...AND CONTINUES TO MOVE EASTWARD.

THE MAIN FORECAST ISSUE REMAINS THE POTENTIAL FOR GUSTY ADVISORY
LEVEL WINDS ACROSS SOME DOWNSLOPE AND EXPOSED HEADLAND AREAS. ONLY
KAMUELA IS REPORTING SUSTAINED WINDS OF 30 MPH OR GREATER AT THIS
TIME...ALTHOUGH SEVERAL OTHER SITES HAVE RECORDED WIND GUSTS IN THE
40S DURING THE PAST FEW HOURS. MODEL GUIDANCE...INCLUDING THE HIGH
RESOLUTION UNIVERSITY OF HAWAII WRF MODEL...DOES STILL INDICATE AN
INCREASE IN BOUNDARY LAYER WINDS LATE TONIGHT INTO MONDAY...WITH
925 MB WINDS REACHING AROUND 35 KNOTS IN SOME AREAS. MODEL
SOUNDINGS ALSO SHOW SOME LOWERING AND STRENGTHENING OF THE
INVERSION DURING THIS TIME...LIKELY IN RESPONSE TO A MID LEVEL
RIDGE BUILDING NORTH OF THE STATE. WILL LEAVE THE WIND ADVISORY
UNCHANGED AT THIS TIME. AGAIN...IT SHOULD BE REITERATED THAT
THE STRONGER WINDS WILL MAINLY AFFECT ONLY SPECIFIC AREAS
IMMEDIATELY DOWNWIND OF THE SMALLER MOUNTAIN RANGES AND OVER
HEADLANDS...WHILE MANY OTHER AREAS WILL SEE CONSIDERABLY LOWER
WIND SPEEDS.

THE TRADES SHOULD RELAX TO MORE MODERATE LEVELS TUESDAY AND
WEDNESDAY AS THE SURFACE HIGH MOVES FURTHER NORTHEAST AND AWAY
FROM THE STATE. ANOTHER WEAKER HIGH WILL BUILD TO THE NORTH OF
OUR AREA WEDNESDAY THROUGH THURSDAY...BUT WOULD NOT EXPECT ANY
SIGNIFICANT WIND PROBLEMS. A STATIC PATTERN WILL THEN DEVELOP
ACROSS THE CENTRAL PACIFIC FOR THE LATE WEEK INTO THE WEEKEND...
WITH AN EAST-WEST HIGH PRESSURE RIDGE NORTH OF THE STATE AND
MODERATE TRADES PREVAILING ACROSS HAWAII.

AS FOR RAIN CHANCES...THE AREA OF HIGHER MOISTURE IS FORECAST TO
SHIFT WEST OF THE STATE BY LATE MONDAY NIGHT OR TUESDAY...WITH A
DRIER AIRMASS THEN PREVAILING THROUGH THE REST OF THE WEEK.
THEREFORE WOULD EXPECT ANOTHER 24 TO 36 HOURS OF A MORE ACTIVE
WINDWARD/MAUKA SHOWER PATTERN WITH SOME LEEWARD SPILLOVER..
FOLLOWED BY MORE LIMITED SHOWER COVERAGE FOCUSING ON WINDWARD AND
MAUKA AREAS THEREAFTER.

&&

.AVIATION...
MODERATE TO STRONG TRADES CONTINUE...SO TO DOES AIRMET TANGO FOR
MECHANICAL TURBULENCE DOWNWIND OF THE MOUNTAINS. THE UPPER LEVEL
TROUGH PASSING OVER THE ISLANDS IS ALSO PRODUCING MODERATE
TURBULENCE AT THE UPPER LEVELS OVER THE ISLANDS. AN AIRMET FOR THIS
TURBULENCE OVER THE ISLANDS HAS BEEN POSTED AND WILL CONTINUE AT
LEAST THROUGH THE NIGHT.

CLOUDS AND SHOWERS BEING CARRIED IN ON THE TRADES WILL BRING MVFR
AND ISOLATED IFR CONDITIONS TO WINDWARD AND MOUNTAIN AREAS. AIRMET
SIERRA HAS BEEN POSTED FOR MOUNTAIN OBSCURATION IN THESE AREAS
OVERNIGHT.

&&

.MARINE...
A 2118Z ASCAT PASS REVEALED 25 KNOT WINDS PREVAILING IN THE
CHANNELS AND IN SOME OF THE OTHER TYPICALLY WINDIER AREAS AROUND
THE HAWAIIAN COASTAL WATERS. THE UH-WRF MODEL INDICATES THAT
WINDS HAVE LIKELY INCREASED FURTHER SINCE 21Z...AND THE SMALL
CRAFT ADVISORY REMAINS POSTED FOR ALL COASTAL WATERS. THE SCA WILL
VERY LIKELY NEED TO BE EXTENDED BEYOND THE CURRENT EXPIRATION TIME
OF 6 PM MONDAY. THERE IS A CHANCE THAT A GALE WARNING COULD BE
NEEDED ON MONDAY IN THE ALENUIHAHA CHANNEL...WITH THE 12Z WRF RUN
SHOWING SUSTAINED WINDS PEAKING AROUND 30 KNOTS IN THE AFTERNOON.
WILL AWAIT FURTHER 00Z CYCLE MODEL DATA BEFORE MAKING A DECISION
ON THIS WITH THE EARLY MONDAY MORNING FORECAST PACKAGE.

THE LATEST WAVEWATCH DATA CONTINUES TO SHOW INCREASING SHORT
PERIOD EASTERLY SWELL FOR TONIGHT AND MONDAY...WHICH MAKES SENSE
AS THE FETCH LENGTH INTO HAWAII INCREASES DUE TO THE MOVEMENT OF
THE STRONG HIGH TO OUR NORTH. A HIGH SURF ADVISORY FOR EAST FACING
SHORES WAS ISSUED EARLIER TODAY AND WILL REMAIN IN EFFECT THROUGH
TUESDAY. NO PROBLEMS THROUGH THE WEEK FOR THE OTHER SHORES...WITH
SMALL NORTHWEST SWELL THROUGH TUESDAY. THE NEXT MODERATE NORTHWEST
SWELL WILL ARRIVE WEDNESDAY AND CONTINUE THROUGH FRIDAY...BUT THE
RESULTING SURF ON NORTH/WEST FACING SHORES WILL REMAIN WELL BELOW
ADVISORY LEVELS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY UNTIL 6 PM HST MONDAY FOR WAIANAE COAST-OAHU
KOOLAU-OLOMANA-WAIANAE MOUNTAINS-LANAI-KAHOOLAWE-MAUI WINDWARD
WEST-MAUI LEEWARD WEST-MAUI CENTRAL VALLEY-SOUTH BIG ISLAND-BIG
ISLAND NORTH AND EAST-KOHALA-BIG ISLAND INTERIOR.

HIGH SURF ADVISORY UNTIL 6 PM HST TUESDAY FOR KAUAI WINDWARD-
OAHU KOOLAU-OLOMANA-MOLOKAI WINDWARD-MAUI WINDWARD WEST-WINDWARD
HALEAKALA-SOUTH BIG ISLAND-BIG ISLAND NORTH AND EAST.

SMALL CRAFT ADVISORY UNTIL 6 PM HST MONDAY FOR ALL HAWAIIAN
WATERS.

&&

$$

DISCUSSION/MARINE...JACOBSON
AVIATION...M BALLARD







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