Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 310618
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST THU JUL 30 2015

.SYNOPSIS...
HIGH PRESSURE TO THE NORTHEAST...AND LOW PRESSURE PASSING TO THE
SOUTH...LIKELY WILL INCREASE TRADE WIND SPEEDS OVER THE WEEKEND.
WINDWARD SHOWERS ALSO WILL INCREASE SLIGHTLY...ESPECIALLY OVER THE
BIG ISLAND. WETTER CONDITIONS OVER MUCH OF THE STATE...AND VARIABLE
WINDS...MAY BE POSSIBLE BY THE MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...
OBSERVATIONS AROUND THE MAIN HAWAIIAN ISLANDS REPORTED SOLIDLY
MODERATE TRADE WINDS BLOWING...THOUGH WIND SPEEDS THROUGH THE
CHANNELS WERE HIGHER...AS WOULD BE EXPECTED FOR GAP FLOW. THE AIR
MASS WAS ON THE MOIST SIDE OF TYPICAL...BUT THE INVERSION LOW UNDER
WEAK RIDGING ALOFT. THUS...RAINFALL WAS MODEST OVERALL...WITH
RECORDED ACCUMULATION FALLING MAINLY OVER WINDWARD SLOPES OF MOST
LARGER ISLANDS...OR LEE SLOPES OF THE BIG ISLAND WHERE SEA BREEZES
PREVAILED. SHOWER ACTIVITY OFFSHORE SHOULD EXPAND OVERNIGHT IN THE
MOIST AIR MASS...BUT DEVELOPING LAND BREEZES MAY LIMIT HOW MUCH OF
THIS NEW ACTIVITY CAN MOVE ASHORE. CIRRUS LAYERS FROM CONVECTION
NEAR THE DATELINE APPEARED MORE DENSE AND WIDESPREAD THAN PREDICTED
EARLIER...SO THE SKY GRID MAY NEED A SLIGHT BOOST OVERNIGHT.

GUIDANCE AGREED IN PREDICTING ONLY GRADUAL CHANGES THROUGH THE
WEEKEND. MOST SOLUTIONS EXPANDED THE RIDGE ALOFT OVERHEAD...THUS
LIMITING SHOWER POTENTIAL. HOWEVER...THE REMNANT LOW FROM FORMER
TROPICAL DEPRESSION EIGHT-E WILL PASS TO THE SOUTH...INCREASING THE
PRESSURE GRADIENT...AND THUS WIND SPEEDS ACROSS THE STATE. GREATER
OROGRAPHIC FORCING IN TURN WILL OPPOSE THE CAPPING EFFECT OF THE
RIDGE ALOFT...AND THE MOISTER AIR MASS SURROUNDING THE PASSING LOW
SHOULD REACH AT LEAST THE BIG ISLAND. THUS...IN THE NET...THE TRADE
WINDS SHOULD INCREASE IN SPEED...AND WINDWARD SHOWERS SHOULD BECOME
SLIGHTLY MORE ACTIVE...AT LEAST OVER THE SOUTH END OF THE STATE.

BY THE MIDDLE OF NEXT WEEK...BIG CHANGES MAY OCCUR. TROPICAL STORM
GUILLERMO CURRENTLY WAS LOCATED ABOUT 2000 MILES EAST-SOUTHEAST OF
HONOLULU IN THE EAST PACIFIC BASIN. GUIDANCE SOLIDLY AGREED IN
PREDICTING THIS SYSTEM TO MOVE WEST-NORTHWEST FOR THE NEXT FEW DAYS.
BY SATURDAY NIGHT...THE NATIONAL HURRICANE CENTER PREDICTED
GUILLERMO TO CROSS 140W INTO THE CENTRAL PACIFIC BASIN. FORECAST
UNCERTAINTY SO FAR IN THE FUTURE ARGUED AGAINST OVERLY DETERMINISTIC
FORECASTS...BUT A CLOSE APPROACH TO THE STATE COULD NOT BE RULED
OUT. IN ANY CASE...THE MIDDLE OF NEXT WEEK PROBABLY WILL BE ON THE
WET SIDE OF CLIMATOLOGY...AND THE PRECISE TRACK OF GUILLERMO MAY
TAKE
THE WIND FIELD VERY FAR INDEED FROM TYPICAL TRADE-WIND CONDITIONS.

&&

.AVIATION...
HIGH PRESSURE N OF THE STATE AND A SERIES OF AREAS OF LOW PRESSURE
TO THE SOUTH OF THE ISLANDS WILL KEEP A BREEZY E TO NE TRADE WIND
FLOW IN PLACE THROUGH FRIDAY. CLOUDS AND SHOWERS WILL FOCUS
PRIMARILY ACROSS MTN AND N THRU E SECTIONS OF THE ISLANDS...AND SOME
BRIEF MVFR CIGS WILL BE POSSIBLE AT PHLI AND PHTO.
ADDITIONALLY...MVFR CIGS WILL LIKELY IMPACT PHNY FROM MID MORNING
FRIDAY INTO THE EARLY EVENING HOURS. ELSEWHERE...VFR CONDITIONS
SHOULD PREVAIL. NO AIRMETS ARE CURRENTLY IN EFFECT...BUT AIRMET
TANGO MAY BE NECESSARY LATER TONIGHT OF FRIDAY.

&&

.MARINE...
A SMALL CRAFT ADVISORY REMAINED IN EFFECT FOR TYPICALLY WINDY
AREAS AROUND MAUI AND THE BIG ISLAND. AS THE REMNANT LOW THAT ONCE
WAS DEPRESSION EIGHT-E PASSES SOUTH OF THE STATE...THE GRADIENT MAY
TIGHTEN ENOUGH TO REQUIRE EXPANSION OF THE ADVISORY TOWARD OAHU AND
KAUAI.

NO MAJOR SWELLS ARE EXPECTED FOR THE NEXT FEW DAYS...SO SURF SHOULD
REMAIN BELOW THE ADVISORY THRESHOLD ALONG ALL SHORES.

THE NATIONAL HURRICANE CENTER IN MIAMI HAS BEEN ISSUING BULLETINS ON
TROPICAL STORM GUILLERMO...LOCATED ABOUT 2000 MILES EAST-SOUTHEAST
OF HONOLULU. THE CURRENT FORECAST PREDICTS GUILLERMO TO MOVE
WEST-NORTHWEST AND STRENGTHEN...LIKELY CROSSING 140W INTO THE
CENTRAL PACIFIC HURRICANE CENTER AREA OF RESPONSIBILITY ON SATURDAY.
ALTHOUGH THE TRACK AND INTENSITY OF THE STORM REMAINED UNCERTAIN SO
FAR IN THE FUTURE...ADVERSE EFFECTS FOR HAWAIIAN COASTAL WATERS NEXT
WEEK COULD NOT BE RULED OUT.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 AM HST SUNDAY FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.

&&

$$

DISCUSSION/MARINE...RYSHKO
AVIATION...JELSEMA





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