Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 011400
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST WED JUL 1 2015

.SYNOPSIS...
A SURFACE RIDGE IN THE VICINITY OF THE ISLANDS WILL KEEP WINDS LIGHT
THROUGH FRIDAY. DAYTIME HEATING WILL PRODUCE LOCAL SEA BREEZES WHICH
WILL CAUSE CLOUDS AND SCATTERED SHOWERS OVER LEEWARD AND INTERIOR
SECTIONS EACH AFTERNOON AND EVENING...FOLLOWED BY LOCAL LAND BREEZES
AND CLEARING SKIES OVERNIGHT. THERE MAY BE A SLIGHT INCREASE IN
AFTERNOON SHOWERS OVER THE NEXT COUPLE OF DAYS AS AN AREA OF
ENHANCED MOISTURE CURRENTLY LOCATED NEAR THE BIG ISLAND PUSHES UP
OVER THE REMAINDER OF THE STATE. THE SURFACE RIDGE IS EXPECTED TO
BUILD NORTH OF THE ISLANDS DURING THE UPCOMING HOLIDAY WEEKEND...
WHICH WILL ALLOW THE TRADES TO GRADUALLY RETURN.

&&

.DISCUSSION...
THE SOUTHWESTERN END OF THE ROUNDED SUBTROPICAL RIDGE IS LOCATED
JUST NORTH OF THE MAIN HAWAIIAN ISLANDS EARLY THIS MORNING. THE
CLOSE PROXIMITY OF THIS FEATURE TO THE STATE IS KEEPING RELATIVELY
LIGHT WINDS IN PLACE ACROSS THE AREA. THIS HAS ALLOWED LOCAL
NIGHTTIME LAND BREEZES TO BECOME ESTABLISHED OVER EACH OF THE
ISLANDS DUE TO NOCTURNAL RADIATIONAL COOLING. ALOFT...A
MID-TROPOSPHERIC TROUGH IS EVIDENT NEAR THE WESTERN END OF THE MAIN
HAWAIIAN ISLAND CHAIN IN WATER VAPOR SATELLITE IMAGERY. THIS TROUGH
ALOFT...WHICH HAS BEEN MOVING SLOWLY TOWARD THE EAST NORTHEAST...HAS
CAUSED THE LOW-LEVEL SUBSIDENCE INVERSION TO BE WEAKER THAN NORMAL.

THE LOCAL LAND BREEZE CIRCULATIONS HAVE CLEARED CLOUDS OVER MOST OF
THE SMALLER ISLANDS OVERNIGHT. LOOKING AT THE LOW-LEVEL MOISTURE
FIELD...THERE IS AN AREA OF ENHANCED TROPICAL MOISTURE BEING
ADVECTED ACROSS MOST OF THE LOWER ELEVATIONS OF THE EASTERN AND
SOUTHEASTERN BIG ISLAND EARLY THIS MORNING. AS A RESULT...LOW CLOUDS
AND SHOWERS REMAIN RELATIVELY ABUNDANT OVER WINDWARD AND
SOUTHEASTERN SECTIONS OF THE BIG ISLAND. SOME OF THIS INCREASED
MOISTURE IS APPROACHING EASTERN MAUI...WHERE LOW CLOUDS AND LIGHT
SHOWERS ARE OCCURRING ALREADY. HOWEVER...SATELLITE DERIVED VALUES OF
PRECIPITABLE WATER /PW/ CONTINUE TO SHOW A ZONE OF RELATIVELY DRY
AIR ACROSS OAHU...MOLOKAI AND LANAI. THERE HAVE BEEN SOME LOW CLOUDS
AND SCATTERED SHOWERS OVER THE COASTAL WATERS WEST AND SOUTHEAST OF
KAUAI...WHICH IS JUST TO THE WEST OF THE ZONE OF RELATIVELY DRY AIR.

THE FORECAST MODELS SHOW THE MID-TROPOSPHERIC TROUGH MOVING SLOWLY
TOWARD THE EAST NORTHEAST THROUGH TONIGHT...BEFORE IT MOVES AWAY
FROM THE AREA ON THURSDAY. IN THE MEANTIME...THIS FEATURE WILL
PRODUCE SLIGHT INSTABILITY IN THE FORM OF WEAK SUBSIDENCE INVERSIONS
THROUGH TONIGHT. THE GUIDANCE ALSO KEEPS THE SURFACE RIDGE IN THE
VICINITY OF THE ISLANDS THROUGH FRIDAY...SO THE BACKGROUND FLOW WILL
REMAIN LIGHT OVER MOST AREAS. THIS WILL CONTINUE TO ALLOW AN
ALTERNATING DIURNAL PATTERN OF LOCAL AFTERNOON SEA BREEZES FOLLOWED
BY LOCAL NIGHTTIME LAND BREEZES THROUGH FRIDAY.

THE LATEST RUN OF THE ECMWF FORECAST MODEL CONTINUES TO SHOW THE
AREA OF SLIGHTLY DRIER AIR WILL REMAIN OVER PORTIONS OF THE CENTRAL
ISLANDS AS IT EDGES SLOWLY NORTHWESTWARD. HOWEVER...MOST OF THE
OTHER MODELS... INCLUDING THE HIGH-RESOLUTION REGIONAL
MODELS...SUGGEST THAT THE ENHANCED MOISTURE CURRENTLY LOCATED EAST
AND SOUTHEAST OF THE BIG ISLAND WILL CONTINUE TO GRADUALLY ADVECT
OVER MOST OF THE SMALLER MAIN HAWAIIAN ISLANDS FROM TODAY INTO
THURSDAY. THE LATEST FORECAST KEEPS PORTIONS OF THE ISLANDS OF MAUI
COUNTY AND THE BIG ISLAND WETTER THAN NORMAL THROUGH THIS
AFTERNOON...WITH SLIGHTLY DRIER CONDITIONS ON OAHU. THE CURRENT
FORECAST ALSO INDICATES INCREASED RAIN CHANCES OVER THE LEEWARD AND
INTERIOR SECTIONS OF MOST OF THE ISLAND CHAIN THURSDAY AND FRIDAY.
WITH RELATIVELY STABLE CONDITIONS EXPECTED AFTER THE MID-LEVEL
TROUGH MOVES AWAY FROM THE AREA...NO SIGNIFICANT HEAVY RAINFALL IS
EXPECTED.

THE LONGER RANGE FORECAST GUIDANCE INDICATES SURFACE RIDGING WILL
BUILD NORTH OF THE STATE STARTING THIS WEEKEND...AND CONTINUE INTO
NEXT WEEK. THE INCREASE OF THE PRESSURE GRADIENT OVER THE STATE WILL
GRADUALLY RETURN THE TRADES TO THE ISLANDS...WITH MODERATE SPEEDS
EXPECTED AGAIN BY MONDAY. THIS SHOULD ALSO BRING A RETURN TO MORE
TYPICAL TRADE WIND WEATHER CONDITIONS...WITH LOW CLOUDS AND TRADE
SHOWERS MAINLY AFFECTING WINDWARD AND MAUKA AREAS...ESPECIALLY
NIGHTS AND MORNINGS.

&&

.AVIATION...
NO AIRMETS ARE IN EFFECT EARLY THIS MORNING. VFR CONDITIONS WILL
PREVAIL OVER MOST AREAS...BUT LOCALIZED MVFR CONDITIONS DUE TO LOW
CLOUDS AND SHRA WILL OCCUR ACROSS EAST AND SOUTHEAST SECTIONS OF THE
BIG ISLAND...AND POSSIBLY EAST MAUI...TODAY. A DIURNAL CONVECTIVE
PATTERN CONSISTING OF LOCALIZED AFTERNOON SEA BREEZES WITH LEEWARD
AND INTERIOR CLOUDS AND ISOLATED SHRA IS ALSO EXPECTED THIS
AFTERNOON. NOTE THAT AN INCREASE IN MOISTURE COMBINED WITH SLIGHTLY
UNSTABLE ATMOSPHERIC CONDITIONS MAY LEAD TO MORE AREAS WITH MVFR DUE
TO AN INCREASE IN COVERAGE OF LOW CLOUDS AND SHRA THIS
AFTERNOON...ESPECIALLY OVER PARTS OF THE LEEWARD BIG ISLAND AND MAUI
COUNTY.

&&

.MARINE...
THE CURRENT FORECAST DOES NOT INDICATE SMALL CRAFT ADVISORY /SCA/
CONDITIONS OVER ANY HAWAIIAN WATERS THROUGH THE UPCOMING HOLIDAY
WEEKEND.

THE WEATHER PATTERN HAS BEEN FAIRLY ACTIVE IN THE SOUTHERN
HEMISPHERE...ESPECIALLY IMMEDIATELY TO THE EAST AND SOUTHEAST OF NEW
ZEALAND. THEREFORE...EXPECT PULSES OF SMALL TO MODERATE SOUTH AND
SOUTHWEST SWELL ENERGY TO AIM TOWARD THE ISLAND CHAIN OVER THE NEXT
SEVERAL DAYS. THIS WILL MAINTAIN SMALL TO MODERATE SURF ALONG SOUTH
FACING SHORES OF THE STATE THROUGH FRIDAY. A SLIGHTLY LARGER
REINFORCING SOUTH SWELL ARRIVING LATE FRIDAY WILL LIKELY PRODUCE A
SLIGHT BUMP IN SURF ALONG SOUTH FACING SHORES DURING THE UPCOMING
HOLIDAY WEEKEND...BUT SURF HEIGHTS ARE EXPECTED TO REMAIN BELOW THE
HIGH SURF ADVISORY CRITERIA.

A CAPTURED FETCH ASSOCIATED WITH THE CIRCULATION AROUND A SURFACE
LOW LOCATED ABOUT MIDWAY BETWEEN THE ALEUTIAN ISLANDS AND HAWAII HAS
BEEN AIMED AT THE MAIN HAWAIIAN ISLAND CHAIN. THIS WILL SEND A SMALL
OUT-OF-SEASON NORTHWEST SWELL...WHICH IS EXPECTED TO REACH THE NORTH
AND WEST FACING SHORES OF MOST ISLANDS LATE TONIGHT...PEAK
THURSDAY...THEN SLOWLY DIMINISH THROUGH FRIDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

HOUSTON







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