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Hawaiian Islands Synoptic Discussion and Guidance

068
FXHW60 PHFO 240630
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST THU OCT 23 2014

.SYNOPSIS...
TRADE WINDS WILL STAY MODERATE THROUGH FRIDAY...THEN WEAKEN THROUGH
THE WEEKEND AND INTO NEXT WEEK AS HIGH PRESSURE TO OUR NORTH
INITIALLY APPROACHES US...THEN MOVES OFF TO THE EAST. CLOUDS AND
SHOWERS WILL CONTINUE TO FAVOR WINDWARD AND MAUKA AREAS...WITH DRIER
CONDITIONS EXPECTED BY EARLY NEXT WEEK. LEEWARD AREAS MAY SEE LOCAL
LAND AND SEA BREEZES MONDAY AND TUESDAY. TRADE WINDS MAY INCREASE
AGAIN LATE NEXT WEEK AS ANOTHER HIGH BUILDS IN TO OUR NORTH.

&&

.DISCUSSION...
A 1032 MB HIGH NEAR 40N160W...FAR NORTH OF THE MAIN HAWAIIAN
ISLANDS...HAS AN ASSOCIATED RIDGE EXTENDING SOUTHEAST THROUGH
30N153W AND 25N140W. THE PRESSURE GRADIENT BETWEEN THIS RIDGE AND
EQUATORIAL LOW PRESSURE STEEPENED THIS AFTERNOON...ALLOWING TRADE
WINDS TO BUILD UP TO MODERATE LEVELS ACROSS LOCAL WATERS. SATELLITE
LOOP SHOWS PATCHES OF BROKEN SHOWERY LOW CLOUDS ARE EMBEDDED WITHIN
TRADE FLOW UPWIND FROM THE ISLANDS...AND ONE OF THESE PATCHES JUST
TO OUR EAST WILL DELIVER INCREASED CLOUD COVER AND TRADE SHOWERS
ACROSS WINDWARD AND MAUKA AREAS TONIGHT. WE EXPECT THIS PATTERN TO
CONTINUE THROUGH FRIDAY AS THE HIGH MOVES SOUTHEASTWARD ALONG THE
RIDGE...INITIALLY APPROACHING THE ISLANDS. BY SATURDAY
AFTERNOON...MODELS SHOW THE HIGH WILL BE SHOVED EASTWARD AS DEEP
TROUGHING IMPINGES ON IT FROM THE NORTHWEST. THE RIDGE WILL REMAIN
NORTH OF THE ISLANDS THROUGH THE FORECAST PERIOD...KEEPING US WITHIN
TRADE FLOW. HOWEVER...WINDS WILL WEAKEN IN RESPONSE TO A PRESSURE
GRADIENT WHICH WILL SLACKEN WITH THE DEPARTURE OF THE HIGH TO THE
EAST. LEEWARD AREAS MAY SEE DEVELOPMENT OF LOCAL LAND AND SEA
BREEZES BY MONDAY OR TUESDAY.

MODELS SHOW HIGH PRESSURE MAY BUILD IN TO THE NORTH OF THE ISLANDS
AGAIN LATE NEXT WEEK AS DEEP TROUGHING TO THE NORTHWEST LIFTS OUT.
CONFIDENCE IS LOW THAT FAR OUT GIVEN THE RUN-TO-RUN VARIABILITY IN
GUIDANCE...BUT IF THE GFS SCENARIO PANS OUT WE MAY HAVE A 1037 MB
HIGH 1200 MILES NORTH OF THE ISLANDS DRIVING MODERATE TO LOCALLY
STRONG TRADE WINDS ACROSS THE ALOHA STATE BY HALLOWEEN.

&&

.AVIATION...
TRADE WIND SHOWERS WILL MAINLY AFFECT WINDWARD AND MAUKA SECTIONS
THIS EVENING AND OVERNIGHT. THE LOWER CLOUDS AND RAIN WILL BRING
TEMPO MVFR CONDITIONS AS THEY MOVE WEST. FOR THE MOST PART...
LEEWARD AREAS WILL REMAIN VFR.

CURRENTLY...THERE ARE NO AIRMETS IN EFFECT.

&&

.MARINE...
A MINOR NORTHERLY SWELL GENERATED BY LOW PRESSURE OVER THE GULF
OF ALASKA LAST WEEKEND ARRIVED TODAY BUT WILL FADE QUICKLY. THIS
LOW WEAKENED BUT HAS BEEN REPLACED BY A STRONGER LOW. MOST OF THE
SWELL ENERGY WITH THIS SECOND LOW WILL BE AIMED TO THE EAST OF THE
ISLANDS...BUT WE SHOULD CATCH THE WESTERN END OF THE SWELL REGION
WHICH WILL BRING A SIMILAR NORTHERLY REINFORCEMENT FOR SATURDAY.

WINDS AND SEAS WILL REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA
THROUGH THE WEEKEND AND INTO NEXT WEEK.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$
POWELL






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