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Hawaiian Islands Synoptic Discussion and Guidance

408
FXHW60 PHFO 030622
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST WED SEP 2 2015

.SYNOPSIS...
A VERY HUMID AND UNSTABLE AIR MASS WILL SUPPORT SPOTTY...BUT LOCALLY
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 WAS DOWN SLIGHTLY FROM THE INSANE
AMOUNTS EARLIER IN THE WEEK...ESPECIALLY OVER KAUAI COUNTY...SLIGHT
CONVERGENCE IN THE WEAK SOUTHEAST SURFACE FLOW AROUND THE STATE
CONTINUED TO ENCOURAGE CONVECTION. A SHALLOW MID-LEVEL TROUGH
EXTENDING SOUTHEAST OVER THE ISLANDS FROM TROPICAL CYCLONE
IGNACIO...AND AFTERNOON SEA BREEZES...ALSO CONTRIBUTED.

THUNDERSTORMS OVER THE BIG ISLAND SHOULD DIMINISH INTO THE
EVENING...AND THOSE OVER THE MAUI COUNTY WINDWARD WATERS MAY WELL
MOVE NORTH OUT OF THE COASTAL WATERS...BUT SHOWERS LIKELY WILL
REMAIN ACTIVE MORE GENERALLY THROUGH THE NIGHT. ANOTHER CONVECTIVE
SURGE...FOLLOWED BY A GRADUAL DECREASE INTO THE EVENING...WILL OCCUR
AS SEA BREEZES BECOME IMPORTANT AGAIN ON THURSDAY.

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...
SEE TC SIGMET SERIES TANGO FOR TROPICAL CYCLONE IGNACIO...LOCATED
ABOUT 375 MILES NORTH OF LIHUE AS OF 5 PM WEDNESDAY AFTERNOON.

A MOIST AND UNSTABLE AIRMASS WILL REMAIN IN PLACE ACROSS HAWAII
OVERNIGHT AND THURSDAY. SHOWERS AND THUNDERSTORMS ARE ALREADY
DIMINISHING WITH LOSS OF DAYTIME HEATING ACROSS THE BIG ISLAND AND
MAUI. HOWEVER...THE POTENTIAL FOR LOCALLY HEAVY SHOWERS AND ISOLATED
THUNDERSTORMS WILL LINGER OVERNIGHT ACROSS MOLOKAI AND OAHU...
SHIFTING WESTWARD TOWARD KAUAI LATE TONIGHT INTO THURSDAY...AS A
LOW LEVEL CONVERGENCE BAND MOVES SLOWLY WEST ACROSS THE STATE. ANY
THUNDERSTORMS ARE LIKELY TO CARRY CB TOPS UP TO FL450...MVFR TO
ISOL IFR CONDITIONS...AND THE POSSIBILITY OF ICING AND TURB.

A SEABREEZE PATTERN WILL PREVAIL ACROSS THE STATE ONCE AGAIN ON
THURSDAY...WITH SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS
DEVELOPING ACROSS THE ISLANDS DUE TO DAYTIME HEATING. MVFR AND
ISOLATED IFR CONDITIONS WILL BE POSSIBLE.

AIRMET SIERRA FOR MOUNTAIN OBSCURATION REMAINS FOR SECTIONS OF THE
BIG ISLAND. THIS AIRMET WILL BE CANCELLED LATER THIS EVENING AS
CONDITIONS IMPROVE. HOWEVER...ADDITIONAL AIRMETS FOR MOUNTAIN
OBSCURATION MAY BE NEEDED ACROSS THE CENTRAL ISLANDS OVERNIGHT.

&&

.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 WAS LARGEST ACROSS KAUAI
AND OAHU...BUT WILL BE DROPPING OFF SIGNIFICANTLY. SURF ALONG
EAST-FACING SHORES WILL APPROACH WARNING LEVELS TONIGHT...AND WAS
EXPECTED TO RISE AGAIN ON THURSDAY. 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 THURSDAY 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...
HIGH SURF WARNING UNTIL 6 PM HST THURSDAY 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