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Hawaiian Islands Synoptic Discussion and Guidance

473
FXHW60 PHFO 180630
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST WED SEP 17 2014

.SYNOPSIS...
LIGHT TRADES WILL ALLOW FOR SEABREEZES TO DEVELOP DURING THE NEXT
FEW DAYS WITH CLOUDS AND SHOWERS RETURNING EACH AFTERNOON AND
EVENING...ESPECIALLY OVER LEEWARD AND INTERIOR AREAS. THE LIGHT
WINDS WILL ALSO KEEP GENERALLY WARM TEMPERATURES ACROSS THE AREA.
INCREASING MOISTURE SOUTH OF THE ISLANDS MAY BRING AN INCREASE IN
RAINFALL OVER THE BIG ISLAND LATE IN THE WEEKEND.

&&

.DISCUSSION...
SCATTERED TO LOCALLY BROKEN CLOUDS WITH EMBEDDED SHOWERS CAN BE
OBSERVED ON RADAR DATA UPSTREAM OF THE SMALLER ISLANDS...MOVING W/SW
TOWARDS THE ALOHA STATE. A WEAK SFC HIGH PRESSURE CIRCULATION N OF
THE ISLANDS IS KEEPING GENTLE TRADES ACROSS THE AREA. ALSO...LATEST
WATER VAPOR SATELLITE IMAGERY SHOWS A WEAK UPPER LEVEL LOW LOCATED
NEAR KAUAI...WHILE A MID/UPPER LEVEL RIDGE IS LOCATED N OF THE
ISLAND CHAIN.

SATELLITE DATA AND LATEST MIMIC/MOISTURE MODEL ANALYSES DEPICT A
SWATH OF ENHANCED MOISTURE ASSOCIATED WITH THE AFOREMENTIONED CLOUDS
UPSTREAM OF THE ISLANDS. THIS ADDITIONAL MOISTURE WILL KEEP BRINGING
SHOWERS AND ISOLATED HEAVY DOWNPOURS OVER THE ISLANDS TONIGHT WITH
BEST CHANCES OF RAINFALL OVER MOUNTAIN AREAS. SOME OF THE LARGER
SHOWERS COULD REACH LEEWARD LOCATIONS AT TIMES.

FOR THE SHORT TERM FORECAST...MODELS ARE IN FAIR AGREEMENT BRINGING
A COLD FRONT PASSAGE ACROSS THE N CENTRAL PACIFIC DURING THE NEXT
FEW DAYS. THIS FRONT WILL FURTHER ERODE THE HIGH TO THE N OF THE
ALOHA STATE AND ALLOW FOR STRONGER SEABREEZE CIRCULATIONS TO DEVELOP
EACH DAY. THIS SYNOPTIC SCENARIO WILL RESULT IN THE DEVELOPMENT OF
AFTERNOON AND EVENING SHOWERS ESPECIALLY OVER LEEWARD AND INTERIOR
AREAS. THE LIGHT WINDS WILL ALSO ALLOW FOR VOLCANIC HAZE TO BUILD
AROUND THE BIG ISLAND...BUT SO FAR IT IS NOT EXPECTED TO REACH THE
SMALLER ISLANDS AS THE LIGHT WINDS SHOULD STILL REMAIN GENERALLY
FROM THE E.

FOR THE UPCOMING WEEKEND...MODELS SHOW A POSSIBLE TROPICAL FEATURE
PASSING TO THE S OF THE ISLANDS BY SUN...BRINGING AN INCREASE IN
MOISTURE AND SHOWERS OVER THE BIG ISLAND. MEANWHILE...THE
AFOREMENTIONED FRONT STALLS ABOUT A COUPLE HUNDRED MILES N OF THE
ALOHA STATE AND GRADUALLY DISSIPATES. THE PRESENCE OF THE DECAYING
FRONT TO THE N AND THE TROPICAL FEATURE TO THE S MAY CAUSE AN
INCREASE IN PRESSURE GRADIENTS ACROSS THE AREA WHICH IN TURN COULD
BRING AN INCREASE IN TRADE FLOW BY LATE SUN AND INTO MON. REGARDLESS
OF THIS SCENARIO...THE HIGH SHOULD BEGIN GAINING STRENGTH EARLY NEXT
WEEK WITH STRONGER TRADES RETURNING BY TUE/WED. THIS WILL BRING
BACK A TRADE WIND WEATHER PATTERN OF CLOUDS AND SHOWERS FAVORING
WINDWARD AND MOUNTAIN AREAS...ESPECIALLY AT NIGHT.

&&

.AVIATION...
BRIEF PERIODS OF MVFR DUE TO REDUCED VIS IN SHRA AND LOWER CEILINGS
ASSOCIATED WITH LOW CLOUDS MAY AFFECT SOME WINDWARD FACING SLOPES
AND HIGHER TERRAIN. ELSEWHERE...LAND BREEZES ARE EXPECTED TO
DOMINATE THROUGH EARLY THURSDAY MORNING...SO VFR CONDITIONS WILL
LIKELY PREVAIL AT ALL ISLAND TERMINALS.

THE LIGHT WINDS WILL RESULT IN LOCAL SEA BREEZE CIRCULATIONS
DEVELOPING AGAIN ON EACH ISLAND FROM LATE THURSDAY MORNING THROUGH
LATE THURSDAY AFTERNOON. EXPECT CLOUD BUILD UPS AND ISOL SHRA OVER
MOST LEEWARD AND INTERIOR SECTIONS OF THE ISLANDS THURSDAY AFTERNOON
AS A RESULT OF THE CONVERGENCE OF THESE SEA BREEZE CIRCULATIONS.


&&

.MARINE...
A PREVAILING MODERATE S SWELL WILL CONTINUE TO SLOWLY SUBSIDE THROUGH
FRIDAY. A SMALL LONG PERIOD SOUTH SWELL WILL BUILD TONIGHT...WHICH
WILL HELP KEEP SMALL SURF ALONG SOUTH FACING SHORES THROUGH THE
WEEKEND. SURF ALONG NORTH FACING SHORES WILL ALSO DECREASE TONIGHT.

A SMALL NW SWELL IS NOW ARRIVING...BUT SURF HEIGHTS OVER N FACING
SHORES ARE EXPECTED TO REMAIN BELOW ADVISORY LEVELS. NO OTHER MAJOR
SWELLS ARE IN THE FORECAST.

WINDS WILL REMAIN LIGHT THROUGH MOST OF THE FORECAST PERIOD. THE
TRADE WINDS WILL BEGIN INCREASING EARLY NEXT WEEK.


&&

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

&&

$$

DISCUSSION/MARINE...REYNES
AVIATION...HOUSTON




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