Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 031329
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST THU SEP 3 2015

.SYNOPSIS...
A VERY HUMID AND UNSTABLE AIR MASS WILL SUPPORT SPOTTY...BUT LOCALLY
VERY HEAVY...SHOWERS AND THUNDERSTORMS INTO THE WEEKEND. WEAK TRADE
WINDS AND SOMEWHAT MORE STABLE CONDITIONS WILL SPREAD FROM THE EAST
ON FRIDAY 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 KAUAI COUNTY...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. LAND BREEZES HELPED TO KEEP MOST OF THE ACTIVITY
OFFSHORE OVERNIGHT...BUT THE INTENSITY OF THE SHOWERS THREATENED
SERIOUS PROBLEMS IF ANY OF THEM WERE TO MAKE IT ASHORE. ANOTHER
CONVECTIVE SURGE...FOLLOWED BY A GRADUAL DECREASE INTO THE
EVENING...WILL OCCUR AS SEA BREEZES BECOME IMPORTANT AGAIN THIS
AFTERNOON.

THE HUMID...HOT...AND LARGELY STAGNANT CONDITIONS ONCE AGAIN WILL
APPROACH...BUT FALL JUST SHORT OF...THE CRITERIA FOR AN EXCESSIVE
HEAT ADVISORY OVER THE NEXT 36 HOURS. SHOWER ACTIVITY WILL HAVE
LITTLE EFFECT ON THIS CONCERN.

BY FRIDAY...A SHIFT IN THE PATTERN OF TROPICAL CYCLONES DRIVING
REGIONAL WEATHER MAY BRING A NOTICEABLE CHANGE. 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. THIS PERIOD OF TRADE WINDS WILL
END BY SUNDAY NIGHT ONCE JIMENA MOVES FAR ENOUGH NORTH...LEAVING
FEEBLE NORTHERLIES IN PLACE...BUT A NUMBER OF SOLUTIONS PREDICTED A
SLIGHTLY DRIER AIR MASS TO REACH THE ISLANDS IN THE MEANTIME.

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...
A MOIST AND UNSTABLE AIRMASS WILL REMAIN IN PLACE ACROSS HAWAII
TODAY...IN THE WAKE OF HURRICANE IGNACIO WHICH IS NOW LOCATED FAR
TO THE NORTH. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE
ONGOING ACROSS PARTS OF THE STATE AS OF 2 AM...AND WILL LIKELY
CONTINUE THROUGH THE DAY AS A COUPLE OF LOW LEVEL CONVERGENCE ZONES
LINGER NEARBY. DEVELOPING SEABREEZES OVER THE ISLANDS WILL PROVIDE
AN ADDITIONAL TRIGGER FOR CONVECTIVE ACTIVITY THIS AFTERNOON. AREAS
OF MVFR AND LOCAL IFR CONDITIONS WILL REMAIN POSSIBLE THROUGH THE
DAY. ANY THUNDERSTORMS ARE LIKELY TO CARRY CB TOPS UP TO FL450...
MVFR/IFR CONDITIONS...AND THE POSSIBILITY OF ICING AND TURB.

AIRMET SIERRA FOR MOUNTAIN OBSCURATION IS IN EFFECT FOR OAHU AND
PORTIONS OF MAUI AT THIS TIME. ADDITIONAL AIRMETS FOR MOUNTAIN
OBSCURATION WILL LIKELY BE NECESSARY THROUGHOUT THE DAY.

&&

.MARINE...
A HIGH SURF WARNING REMAINED IN EFFECT FOR EAST-FACING SHORES OF
MOST ISLANDS. THE LARGE SURF WAS DUE TO A MIX OF DECLINING NORTHERLY
SWELL FROM IGNACIO...AND A BUILDING EAST SWELL FROM DISTANT
HURRICANE JIMENA. THE IGNACIO SWELL STILL WILL BE DROPPING OFF
SIGNIFICANTLY. SURF ALONG EAST-FACING SHORES WAS EXPECTED TO RISE
AGAIN TODAY. EVEN IF THE SWELL DROPS SLIGHTLY...EAST-SHORE SURF WILL
REMAIN NEAR WARNING LEVELS THROUGH AT LEAST THE WEEKEND...AND LIKELY
INTO EARLY NEXT WEEK. THE HIGH SURF WARNING PROBABLY WILL NEED
EXTENSION BEYOND THIS AFTERNOON.

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 ADVISORY LEVELS THIS WEEK.

LONG-PERIOD SWELLS FROM THE SOUTH-SOUTHWEST MAY 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 THIS EVENING FOR ALL HAWAII ISLANDS.

HIGH SURF WARNING UNTIL 6 PM HST THIS EVENING 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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