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Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office

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Hawaiian Islands Synoptic Discussion and Guidance

404
FXHW60 PHFO 040603
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST THU SEP 3 2015

.SYNOPSIS...
A HUMID AND UNSTABLE AIR MASS WILL SUPPORT SPOTTY...BUT LOCALLY
VERY HEAVY...SHOWERS AND THUNDERSTORMS INTO FRIDAY. WEAK TRADE WINDS
AND SOMEWHAT MORE STABLE CONDITIONS WILL SPREAD FROM THE EAST ON
FRIDAY NIGHT AND SATURDAY...THOUGH THE WEATHER WILL REMAIN HOTTER
AND MORE HUMID THAN USUAL. PREVAILING WINDS WILL DIMINISH INTO NEXT
WEEK...LEADING TO STAGNANT CONDITIONS AND INCREASED AFTERNOON
SHOWERS AGAIN.

&&

.DISCUSSION...
ALTHOUGH PRECIPITABLE WATER REMAINED DOWN SLIGHTLY FROM THE INSANE
VALUES EARLIER IN THE WEEK...ESPECIALLY OVER THE BIG ISLAND...SLIGHT
CONVERGENCE IN THE WEAK SOUTHEAST SURFACE FLOW AROUND THE STATE
CONTINUED TO ENCOURAGE DEEP CONVECTION. A SHALLOW MID-LEVEL TROUGH
EXTENDING SOUTHEAST OVER THE ISLANDS FROM TROPICAL CYCLONE IGNACIO
ALSO CONTRIBUTED.

MUCH OF THE CONVECTION SHIFTED OFFSHORE DURING THE LATE AFTERNOON...
BUT IT WILL BE SOME HOURS YET BEFORE LAND BREEZES BECOME STRONG
ENOUGH TO ENFORCE THIS CHANGE AT ALL RELIABLY. IN PARTICULAR...THE
CONVECTIVE PLUME EXTENDING NORTHWEST FROM MOLOKAI THREATENED TO MOVE
OVER OAHU.

ON FRIDAY...A SHIFT IN THE PATTERN OF TROPICAL CYCLONES DRIVING
REGIONAL WEATHER MAY BRING A NOTICEABLE CHANGE FROM THE HUMID AND
STAGNANT CONDITIONS. ALTHOUGH TROPICAL CYCLONE JIMENA WILL REMAIN
FAR ENOUGH AWAY NOT TO AFFECT THE ISLANDS DIRECTLY...A SWATH OF
NORTHEAST WINDS WILL EXTEND PAST THE NORTH EDGE OF THE STORM AND
OVER THE STATE. GUIDANCE PREDICTED FAIRLY MODEST WIND SPEEDS...BUT
THEY STAND A GOOD CHANCE OF BEING STRONGER THAN THE CURRENT
PREVAILING FLOW. MOST SOLUTIONS ALSO PREDICTED A SLIGHTLY DRIER AIR
MASS TO ADVECT IN ON THE WINDS. CONVERGENCE ALONG THE LEADING EDGE
OF THE NEW AIR MASS MAY ENCOURAGE A SLIGHT BURST OF SHOWERS AT
FIRST...BUT BY SATURDAY SUBSIDENCE AROUND JIMENA WILL HELP TO
STABILIZE CONDITIONS.

THIS PERIOD OF TRADE WINDS WILL END BY SUNDAY NIGHT ONCE JIMENA
MOVES FAR ENOUGH NORTH...LEAVING FEEBLE NORTHERLIES IN PLACE.
STAGNANT FLOW INTO NEXT WEEK WILL PERMIT EVAPORATION TO MOISTEN THE
AIR MASS AGAIN...AND DIURNAL EFFECTS WILL PREVAIL. CONDITIONS DURING
THE LATTER PART OF NEXT WEEK DEPENDED HEAVILY ON THE PRECISE TRACK
OF JIMENA.

&&

.AVIATION...
AN AREA OF LOW LEVEL CONVERGENCE DRIFTING WESTWARD OVER THE CENTRAL
AND WESTERN PART OF THE STATE....COMBINED WITH AN UPPER LEVEL TROUGH
AND COPIOUS TROPICAL MOISTURE...WILL CONTINUE TO GENERATE SCATTERED
HEAVY SHOWERS AND ISOLATED THUNDERSTORMS OVERNIGHT AND FRIDAY. AREAS
OF MVFR WITH LOCALIZED IFR...ALONG WITH LIGHTNING...TURB AND ICING
WILL BE POSSIBLE WITH ANY THUNDERSTORMS.

AIRMET SIERRA FOR MTN OBSC IS CURRENTLY POSTED FOR THE ENTIRE STATE.
THIS AIRMET WILL LIKELY BE DROPPED FOR SOME ISLANDS DURING THE
EVENING...BUT ADDITIONAL AIRMETS WILL LIKELY BE NEEDED AT TIMES LATE
TONIGHT AND FRIDAY.

&&

.MARINE...
INCOMING EAST SWELL FROM HURRICANE JIMENA CONTINUED TO REQUIRE A
HIGH SURF WARNING FOR EAST-FACING SHORES OF MOST ISLANDS. EAST-SHORE
SURF WILL REMAIN NEAR WARNING LEVELS THROUGH THE WEEKEND...AND
LIKELY INTO EARLY NEXT WEEK.

A SMALL CRAFT ADVISORY ALSO REMAINED IN EFFECT THROUGH FRIDAY
AFTERNOON FOR HAZARDOUS SEAS PRODUCED BY THE SWELLS FROM IGNACIO AND
JIMENA. WINDS ARE EXPECTED TO REMAIN BELOW THE ADVISORY THRESHOLD
THIS WEEK.

A LONG-PERIOD SWELL FROM THE SOUTH-SOUTHWEST WILL PRODUCE
ADVISORY-LEVEL SURF ALONG SOUTH-FACING SHORES THIS WEEKEND. PLEASE
REFER TO THE LATEST COLLABORATIVE NEARSHORE SWELL AND WIND FORECAST
/SRDHFO/ FOR MORE DETAILS ON THE SWELLS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH FRIDAY AFTERNOON FOR ALL HAWAII ISLANDS.

HIGH SURF ADVISORY FROM 6 AM FRIDAY TO 6 PM HST SATURDAY FOR
NIIHAU-KAUAI LEEWARD-OAHU SOUTH SHORE-WAIANAE COAST-LANAI MAKAI-
KAHOOLAWE-MAUI LEEWARD WEST-LEEWARD HALEAKALA-KONA.

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

SMALL CRAFT ADVISORY UNTIL 6 PM HST FRIDAY FOR KAUAI NORTHWEST
WATERS-KAUAI WINDWARD WATERS-KAUAI CHANNEL-OAHU WINDWARD WATERS-
KAIWI CHANNEL-MAUI COUNTY WINDWARD WATERS-PAILOLO CHANNEL-ALENUIHAHA
CHANNEL-BIG ISLAND WINDWARD WATERS-BIG ISLAND SOUTHEAST WATERS.

&&

$$

DISCUSSION/MARINE...RYSHKO
AVIATION...JACOBSON




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