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RH80 %
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Hawaiian Islands Synoptic Discussion and Guidance

447
FXHW60 PHFO 271949
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
949 AM HST THU AUG 27 2015

.SYNOPSIS...
HOT AND HUMID CONDITIONS WILL CONTINUE. LOCALLY HEAVY SHOWERS AND
ISOLATED THUNDERSTORMS ARE EXPECTED THIS AFTERNOON WITH FLASH
FLOODING POSSIBLE. VARIABLE WINDS WITH AFTERNOON SEA BREEZES TODAY
WILL GIVE WAY TO WEAK TRADE WINDS FRIDAY AND SATURDAY. ALTHOUGH
SHOWERS WILL FAVOR WINDWARD AND MAUKA AREAS... AFTERNOON CLOUDS
AND SPOTTY SHOWERS CAN BE EXPECTED OVER LEEWARD AREAS. HURRICANE
IGNACIO WILL APPROACH THE STATE LATE IN THE WEEKEND AND MAY
THREATEN THE ISLANDS DURING THE FIRST PART OF NEXT WEEK.

&&

.DISCUSSION...
THE ATMOSPHERE AROUND THE STATE REMAINS MOIST AND UNSTABLE WITH
DEW POINTS IN THE MID 70/S AND A MID TO UPPER LEVEL TROUGH
LINGERING JUST NORTH OF THE ISLANDS. DAYTIME HEATING AND SEA
BREEZE CONVERGENCE WILL BE ENOUGH OF A TRIGGER TO SET OFF ANOTHER
BOUT OF HEAVY SHOWERS AND ISOLATED THUNDERSTORMS LATER THIS
AFTERNOON. A FLASH FLOOD WATCH REMAINS IN EFFECT THROUGH THE
AFTERNOON...AND WITH THE GROUND ALREADY SATURATED...FLOODING COULD
HAPPEN QUICKLY. SHOWERS WILL ONCE AGAIN TAPER OFF DURING THE
EVENING.

LIGHT TRADE WINDS WILL PICK UP FRIDAY AND REMAIN INTO SATURDAY AS
HIGH PRESSURE BUILDS SLOWLY NORTH OF THE STATE. SHOWERS WILL FAVOR
WINDWARD AND MAUKA AREAS AT NIGHT AND THROUGH THE MORNING HOURS.
HOWEVER...THE TRADES WILL BE WEAK ENOUGH TO ALLOW AFTERNOON SEA
BREEZES TO FORM ALONG LEEWARD COASTS. THE SEA BREEZES AND DAYTIME
HEATING WILL LIKELY SHIFT RAINFALL FOCUS TO CENTRAL AND LEEWARD
LOCATIONS IN THE AFTERNOON. SUNDAY...TRADE WINDS ARE EXPECTED TO
INCREASE A NOTCH AND SHOULD BE SUFFICIENTLY STRONG ENOUGH TO
PROHIBIT WIDESPREAD AFTERNOON SEA BREEZES AND ASSOCIATED CONVECTIVE
ACTIVITY.

FORECAST UNCERTAINTY INCREASES SIGNIFICANTLY ON MONDAY AND
TUESDAY...HINGING ON THE EVENTUAL TRACK OF HURRICANE IGNACIO.
HURRICANE IGNACIO WILL APPROACH THE BIG ISLAND LATE IN THE
WEEKEND AND MAY THREATEN THE ISLANDS EARLY NEXT WEEK. FORECAST
TRACK ERRORS AT THAT TIME ARE MORE THAN A COUPLE HUNDRED
MILES...SO IT IS TOO EARLY TO TELL WHAT THE DIRECT IMPACTS WILL
BE. EVERYONE IN THE STATE SHOULD MONITOR THE PROGRESS OF IGNACIO
DURING THE NEXT SEVERAL DAYS...AND THE NATIONAL WEATHER SERVICE
URGES INDIVIDUALS TO HAVE AN ACTION PLAN IN CASE IGNACIO...OR ANY
HURRICANE...THREATENS.

&&

.AVIATION...
A SURFACE TROUGH NE OF THE CENTRAL ISLANDS WILL LINGER THROUGH THE
DAY. THE TROUGH IS HELPING TO PRODUCE LIGHT FLOW OVER THE STATE
WITH A SLIGHT HINT OF NE FLOW NEAR THE WESTERN END AND LIGHT SE
FLOW NEAR THE EASTERN. THIS FLOW WILL REMAIN LIGHT ENOUGH TO
PROMOTE THE DEVELOPMENT OF SEA BREEZES. MOSTLY CLEAR SKIES THIS
MORNING WILL PROMOTE DAYTIME HEATING AND GIVE WAY TO AFTERNOON CLOUD
BUILDUPS WITH A SLIGHT CHANCE OF THUNDERSTORMS ACROSS THE ISLANDS.

THE ATMOSPHERE SURROUNDING THE STATE REMAINS MOIST AND UNSTABLE
WITH PRECIPITABLE WATER VALUES RANGING FROM 1.78 TO 1.97 INCHES
RESPECTIVELY AT PHTO AND PHLI. SHOWERS THIS AFTERNOON HAVE THE
POTENTIAL TO BE HEAVY AT TIMES WITH MVFR TO ISOL IFR CONDITIONS
LIKELY. EXPECT CLOUDS AND SHOWERS TO HAVE TCU TOPS REACHING FL250
AND POSSIBLE CB TOPS TO FL350-450.

AS OF 20Z THERE ARE NO AIRMETS IN EFFECT...HOWEVER WILL BE POSTED AS
NEEDED THIS AFTERNOON UNDER CONVECTIVE ACTIVITY.

&&

.MARINE...
ASIDE FROM A SLIGHT CHANCE OF THUNDERSTORMS TODAY...THE MAIN CONCERN
WILL BE A MODERATE WEST TO WEST-NORTHWEST SWELL DURING THE NEXT
SEVERAL DAYS. THE HANALEI BUOY HAS BEEN PICKING UP AN INCREASE IN
LONG PERIOD ENERGY OVERNIGHT. WHILE THE IMPACTS OF THIS SWELL WILL
BE MODEST ON MOST ISLANDS...WE WILL HAVE TO MONITOR THE BUOYS
TODAY...SINCE ADVISORY LEVEL SURF COULD DEVELOP ALONG WEST FACING
SHORES OF THE BIG ISLAND AS EARLY AS TONIGHT AND LAST THROUGH
SATURDAY.

UNCERTAINTY IS VERY HIGH REGARDING THE POTENTIAL IMPACTS ON THE
STATE FROM HURRICANE IGNACIO EARLY NEXT WEEK...BUT WE ARE CONFIDENT
THAT AN EAST-SOUTHEAST WILL ARRIVE SATURDAY. THIS SWELL WILL
MAINLY IMPACT THE BIG ISLAND AND MAUI...WHERE ADVISORY LEVEL SURF
IS EXPECTED ALONG EAST FACING SHORES SATURDAY THEN LIKELY RISE TO
WARNING LEVELS SUNDAY. SOME OF THIS SWELL ENERGY WILL EVENTUALLY
IMPACT THE REST OF THE STATE.

WINDS AND SEAS WILL REMAIN BELOW SMALL CRAFT ADVISORY LEVELS THROUGH
SATURDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH UNTIL 6 PM HST THIS EVENING FOR NIIHAU-KAUAI-
OAHU-MOLOKAI-LANAI-MAUI-BIG ISLAND.


&&

$$

MORRISON...PUBLIC
EATON...AVIATION