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Hawaiian Islands Synoptic Discussion and Guidance

791
FXHW60 PHFO 200643
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
843 PM HST SAT APR 19 2014

.SYNOPSIS...
TRADE WINDS WILL INCREASE SUNDAY...THEN REMAIN STRONG SUNDAY
NIGHT AND MONDAY BEFORE DROPPING BACK TO MODERATE LEVELS TUESDAY.
SHOWERS WILL FOCUS OVER WINDWARD SLOPES WITH LEEWARD AREAS SEEING
ISOLATED SHOWERS.

&&

.DISCUSSION...
RADAR AND RAIN GAUGE DATA INDICATE VERY LITTLE SHOWER ACTIVITY
ACROSS THE STATE DURING THE PAST SEVERAL HOURS. THE 00Z SOUNDINGS
WERE NOT CHANGED MUCH FROM 12 HOURS EARLIER...WITH THE INVERSION
BASED BETWEEN 5500 AND 7500 FEET. MODERATE LOW LEVEL TRADE FLOW OF
AROUND 20 KNOTS PREVAILS AS PER THE LIHUE SOUNDING AND 88D VWP
DATA. SATELLITE IMAGERY CONTINUES TO SHOW ABUNDANT MID/HIGH LEVEL
CLOUDINESS STREAMING NORTHWARD ACROSS THE REGION...TO THE EAST OF
A MID/UPPER LEVEL TROUGH CENTERED SEVERAL HUNDRED MILES TO THE
SOUTHWEST. AT THE SURFACE...A 1030 MB HIGH IS CENTERED ABOUT 1000
MILES NNW OF KAUAI...AND IS BUILDING EASTWARD.

IN THE NEAR TERM...WILL BE PUSHING BACK THE START TIME OF THE
EXISTING WIND ADVISORY A FEW HOURS UNTIL 10 AM SUNDAY...AS THE
LATEST GUIDANCE AND EXTRAPOLATION FROM CURRENT SURFACE OBS
INDICATES THAT IT IS UNLIKELY THAT WE WILL SEE ADVISORY LEVEL
WINDS BEFORE THAT TIME. THE 12Z LOCAL WRF RUN SUGGESTS THAT THE
STRONGEST WINDS WILL LIKELY OCCUR SUNDAY NIGHT THROUGH MONDAY...
BUT THERE IS STILL THE POTENTIAL FOR AT LEAST ISOLATED ADVISORY
WINDS IN SOME AREAS SUNDAY AFTERNOON.

OTHERWISE...MIMIC-TPW SATELLITE IMAGERY AND MODEL DATA CONTINUE
TO SUGGEST THAT AN AREA OF SOMEWHAT ENHANCED MOISTURE WILL MOVE
WESTWARD INTO THE STATE LATE TONIGHT INTO SUNDAY MORNING. WOULD
EXPECT THIS ADDITIONAL MOISTURE WITHIN BUILDING TRADE FLOW TO
SUPPORT INCREASED SHOWER ACTIVITY ACROSS WINDWARD AND MAUKA
AREAS...WITH SPILLOVER OF AT LEAST ISOLATED SHOWERS INTO SOME
LEEWARD SECTIONS.

STRONG TRADES WILL PREVAIL SUNDAY NIGHT AND MONDAY AS HIGH
PRESSURE PASSES BY TO OUR NORTH...THEN TRADES SHOULD FALL BACK TO
MODERATE LEVELS ON TUESDAY WITH THE HIGH MOVING FURTHER AWAY TO
THE NORTHEAST. THE OTHER PLAYER IN OUR WEATHER DURING THE EARLY TO
MID WEEK PERIOD WILL BE A SLOW MOVING MID/UPPER TROUGH TO THE
SOUTHWEST OF THE STATE. GUIDANCE IS A BIT MORE EMPHATIC WITH
MAINTAINING THIS FEATURE IN THE MID LEVELS (500 MB) THAN IT WAS
YESTERDAY...BUT SHOWS LITTLE REFLECTION IN THE LOWER LEVELS WITH A
DISTINCT DRY LAYER MAINTAINED BETWEEN THE MOISTURE ALOFT AND THE
MOIST TRADE FLOW AT LOW LEVELS. AT THIS POINT IT STILL APPEARS
THAT THERE WILL BE LITTLE IMPACT FROM THIS FEATURE ON SENSIBLE
WEATHER ASIDE FROM CONTINUED MID/HIGH CLOUDINESS...BUT THIS IS
SOMETHING TO KEEP AN EYE ON THROUGH THE NEXT FEW DAYS.

LONGER RANGE GUIDANCE INDICATES A STATIC PATTERN ACROSS THE
CENTRAL PACIFIC. MODERATE TRADES WITH PRIMARILY WINDWARD AND
MAUKA SHOWERS ARE LIKELY TO CONTINUE ACROSS HAWAII FROM
WEDNESDAY AT LEAST THROUGH THE END OF NEXT WEEK.

&&

.AVIATION...
TRADE WIND FLOW CONTINUES...RESULTING IN AIRMET TANGO FOR TURBULENCE
TO THE LEE OF THE ALL ISLANDS. TRADES ARE EXPECTED TO CONTINUE
THROUGH THE WEEKEND...SO EXPECTING THE AIRMET TO ALSO CONTINUE.

SHOWER ACTIVITY MAY INCREASE AND BECOME WIDESPREAD TOWARDS DAYBREAK
SUNDAY WHERE AIRMET SIERRA FOR MTN OBSC MAY BE NEEDED. BUT BETWEEN
NOW AND THEN...VFR RULES WITH BRIEF MVFR CEILINGS AND VIS ASSOCIATED
WITH THE SHOWERS RIDING IN WITH THE TRADES. THESE SHOWERS WILL BE
FAVORING THE WINDWARD AND MTN AREAS...WITH A FEW OF THESE SHOWERS
DRIFTING INTO THE LEEWARD AREAS OF THE SMALLER ISLANDS.

&&

.MARINE...
A SMALL CRAFT ADVISORY REMAINS POSTED FOR ALL HAWAIIAN COASTAL
WATERS DUE TO GUSTY TRADE WINDS AND ROUGH SEAS. WINDS WILL
INCREASE FURTHER SUNDAY INTO MONDAY...AS HIGH PRESSURE STRENGTHENS
TO OUR NORTH. WINDS MAY REACH NEAR GALE FORCE AT TIMES SUNDAY
NIGHT THROUGH MONDAY IN THE ALENUIHAHA CHANNEL.

STRENGTHENING TRADE WINDS WILL PRODUCE SHORT PERIOD...CHOPPY SURF
ALONG EAST FACING SHORES...POSSIBLE REACHING ADVISORY LEVELS BY
SUNDAY EVENING...AND LIKELY REACHING ADVISORY LEVELS BY MONDAY.
OTHERWISE...A SMALL TO MODERATE NORTHWEST SWELL WILL CONTINUE
TONIGHT INTO SUNDAY...THEN DECLINE SUNDAY EVENING. ANOTHER
MODERATE NORTHWEST SWELL IS EXPECTED TO ARRIVE WEDNESDAY NIGHT AND
CONTINUE THROUGH FRIDAY. RESULTING SURF ON NORTH AND WEST FACING
SHORES WILL REMAIN WELL BELOW ADVISORY LEVELS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY FROM 10 AM SUNDAY TO 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.

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

&&

$$

DISCUSSION/MARINE...JACOBSON
AVIATION...LAU





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