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Hawaiian Islands Synoptic Discussion and Guidance

451
FXHW60 PHFO 292010
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1010 AM HST FRI MAY 29 2015

.SYNOPSIS...
LIGHT TO MODERATE TRADE WINDS WILL RETURN TO MOST AREAS THIS
WEEKEND...BUT WINDS WILL REMAIN LIGHT AND VARIABLE OVER THE BIG
ISLAND. THE TRADE WINDS WILL DELIVER CLOUDS AND A FEW SHOWERS TO
WINDWARD SLOPES AND COASTS ESPECIALLY DURING NIGHTS AND MORNINGS...
WHILE LEEWARD AREAS MAY SEE A FEW AFTERNOON CLOUDS. TRADE WINDS MAY
DIMINISH AGAIN EARLY NEXT WEEK AS A PERSISTENT TROUGH NORTHEAST OF
THE BIG ISLAND MOVES OVER THE SMALLER ISLANDS.

&&

.DISCUSSION...
LIGHT WINDS ALLOWED SKIES TO CLEAR EARLY THIS MORNING...BUT THAT
WAS RELATIVELY SHORT-LIVED...AS SKIES HAVE ALREADY BEGIN TO CLOUD-UP
OVER THE ISLANDS WITHIN THE LAST HOUR. THE LIGHT WINDS ARE DUE TO A
PERSISTENT SURFACE TROUGH THAT EXTENDS NE FROM NEAR THE BIG
ISLAND...AND HIGH PRESSURE CENTERED TO THE DISTANT NW. THIS LAYOUT
IS KEEPING THE LOCAL SURFACE PRESSURE GRADIENT ON THE LOOSE SIDE...
AND IS LEADING TO LIGHT AND VARIABLE WINDS OVER THE E END OF THE
STATE...WITH GENTLE TO LOCALLY MODERATE NE WINDS OVER THE W END.
MIMIC-TPW SATELLITE IMAGERY DEPICTS A LARGE AREA OF HIGH ATMOSPHERIC
MOISTURE CONTENT EXTENDING FAR TO THE ENE OF THE BIG ISLAND...WITH A
TAIL OF ABOVE NORMAL MOISTURE TRAILING TO THE WSW ACROSS MUCH OF THE
STATE. THE 12Z SOUNDINGS SHOWED VERY LITTLE CHANGE DURING THE
PREVIOUS 12 HOURS...WITH INVERSIONS BASED AROUND 8K FEET...AND
SLIGHTLY ABOVE NORMAL PWATS NEAR 1.35 INCHES.

STRONG W/NW WINDS CONTINUE ON THE BIG ISLAND SUMMITS DUE TO A
MID-LEVEL TROUGH TO THE N...WITH THE CFHT SENSOR SHOWING SUSTAINED
WINDS CONSISTENTLY AROUND 50 MPH WITH GUSTS NEAR 60 MPH AT TIMES
DURING THE NIGHT. A WIND ADVISORY REMAINS POSTED FOR THE SUMMITS
THROUGH 6 PM TODAY...AND THE GRADIENT ALOFT SHOULD WEAKEN
SUFFICIENTLY BY THAT TIME TO ALLOW THE ADVISORY TO EXPIRE.

TODAY SHOULD BE SIMILAR TO THURSDAY...WITH NE BACKGROUND FLOW AND
LOCALIZED SEA BREEZES OVER THE W ISLANDS...AND LIGHT FLOW WITH MORE
WIDESPREAD SEA BREEZES OVER THE EASTERN ISLANDS. AREAS OF ABOVE
NORMAL MOISTURE LINGERING AROUND THE STATE MAY PRODUCE MORE
CLOUDINESS AND A BIT MORE SHOWER ACTIVITY THAN WOULD OTHERWISE BE
THE CASE ACROSS INTERIOR AND LEEWARD AREAS ONCE AGAIN THIS AFTERNOON.

LIGHT TO MODERATE TRADES WILL RETURN TO MOST OF THE STATE THIS
WEEKEND...AS HIGH PRESSURE BUILDS TO THE NW. GUIDANCE HAS TRENDED
STRONGER WITH THE TRADE WIND FLOW ACROSS THE SMALLER ISLANDS ON
SATURDAY...PARTICULARLY KAUAI/OAHU...WITH LIGHTER WINDS AROUND
THE BIG ISLAND AS THE SURFACE TROUGH LINGERS TO THE NE. CONTINUED
ABOVE NORMAL MOISTURE AND RELATIVELY WEAK INVERSIONS SHOULD ALLOW
FOR ACTIVE TRADE SHOWERS ACROSS WINDWARD AND MAUKA AREAS. SEA
BREEZES ON THE SMALLER ISLANDS WILL MAY BE LIMITED DUE TO THE
EXPECTED STRONGER TRADES...BUT WITH THE EXTRA MOISTURE IN PLACE WE
COULD STILL SEE ISOLATED TO WIDELY SCATTERED AFTERNOON SHOWERS
DEVELOP ACROSS SOME INTERIOR/LEEWARD AREAS...ESPECIALLY ON MAUI. THE
KONA COAST OF THE BIG ISLAND SHOULD SEE SOMEWHAT BETTER RAIN
CHANCES...AS IS OFTEN THE CASE DURING THE SUMMER MONTHS.

TRADES MAY WEAKEN SLIGHTLY EARLY NEXT WEEK AS THE SFC HIGH SHIFTS
NE...AND THE SURFACE TROUGH NE OF THE BIG ISLAND SHIFTS WESTWARD
OVER THE OTHER ISLANDS. IT MAY BRIEFLY SHARPEN IN RESPONSE TO A
PROGRESSIVE MID-LEVEL TROUGH PASSING FROM W TO E ACROSS THE AREA.
THIS COMBINED WITH CONTINUED ABOVE NORMAL MOISTURE COULD RESULT IN
ENHANCED SHOWERS...BOTH IN THE TYPICAL WINDWARD/MAUKA AREAS...AS
WELL AS OVER INTERIOR/LEEWARD AREAS ALONG LOCAL SEA BREEZES DURING
THE AFTERNOONS. LATEST MODEL GUIDANCE INDICATES A FAIRLY SEASONABLE
TRADE WIND PATTERN FOR THE MIDDLE AND LATTER PART OF THE NEXT
WEEK...WITH LIGHT TO MODERATE TRADE WINDS.

&&

.AVIATION...
OVERNIGHT LAND BREEZES CLEARED OUT MOST ISLAND AREAS LAST NIGHT.
LIGHT TRADE WIND FLOW WILL ALLOW FOR LOCALIZED SEA BREEZES TO SET UP
AND INTERIOR CLOUDS AND SHOWERS TO BUILD THIS AFTERNOON. SOME
SHOWERS MAY INTRODUCE FLEETING PERIODS OF MVFR. NO AIRMETS ARE
EXPECTED THROUGH THE AFTERNOON.

AN AREA OF ENHANCED MOISTURE IS APPROXIMATELY 250 MILES NE OF THE
SMALLER ISLANDS AND IS FORECAST TO BE NEAR THE ISLANDS BY SATURDAY
MORNING. DURING THAT TIME...CLOUDS AND SHOWERS WILL FOCUS OVER
WINDWARD AND MOUNTAIN AREAS AND MOUNTAIN OBSCURATIONS MAY COME INTO
EFFECT.

&&

.MARINE...
A RELATIVELY SMALL LONG-PERIOD S SWELL WILL PERSIST THROUGH
SATURDAY...WITH SURF BELOW ADVISORY LEVELS. A LONGER-PERIOD SSW
SWELL EXPECTED SUNDAY IS LIKELY TO PRODUCE ADVISORY-LEVEL SURF ALONG
S FACING SHORES INTO TUESDAY...WITH PEAK OPEN OCEAN SWELL HEIGHTS
NEAR 5 FEET. THIS SWELL MAY CAUSE SURGES IN HARBORS EXPOSED TO THE
S...AND BREAKING WAVES IN AND NEAR S-FACING CHANNEL ENTRANCES.
MARINERS AND BEACHGOERS SHOULD BE ALERT TO THE FACT THAT THIS IS
LIKELY TO BE THE LARGEST S SWELL OF THE SEASON THUS FAR.
OTHERWISE...SMALL AND RELATIVELY SHORT-PERIOD WNW SWELLS WILL
ARRIVE OVER THE NEXT COUPLE OF DAYS...SUPPORTING SMALL SURF ALONG N
FACING SHORES. WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL
CRAFT ADVISORY /SCA/ LEVELS THROUGH THE WEEKEND...AND INTO EARLY
NEXT WEEK...AFTER WHICH STRONGER TRADE WINDS MAY NECESSITATE A SCA
ISSUANCE.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY UNTIL 6 PM HST THIS EVENING FOR BIG ISLAND SUMMITS.

&&

$$

DISCUSSION/MARINE...BIRCHARD
AVIATION...EATON




554
FXHW60 PHFO 292010
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1010 AM HST FRI MAY 29 2015

.SYNOPSIS...
LIGHT TO MODERATE TRADE WINDS WILL RETURN TO MOST AREAS THIS
WEEKEND...BUT WINDS WILL REMAIN LIGHT AND VARIABLE OVER THE BIG
ISLAND. THE TRADE WINDS WILL DELIVER CLOUDS AND A FEW SHOWERS TO
WINDWARD SLOPES AND COASTS ESPECIALLY DURING NIGHTS AND MORNINGS...
WHILE LEEWARD AREAS MAY SEE A FEW AFTERNOON CLOUDS. TRADE WINDS MAY
DIMINISH AGAIN EARLY NEXT WEEK AS A PERSISTENT TROUGH NORTHEAST OF
THE BIG ISLAND MOVES OVER THE SMALLER ISLANDS.

&&

.DISCUSSION...
LIGHT WINDS ALLOWED SKIES TO CLEAR EARLY THIS MORNING...BUT THAT
WAS RELATIVELY SHORT-LIVED...AS SKIES HAVE ALREADY BEGIN TO CLOUD-UP
OVER THE ISLANDS WITHIN THE LAST HOUR. THE LIGHT WINDS ARE DUE TO A
PERSISTENT SURFACE TROUGH THAT EXTENDS NE FROM NEAR THE BIG
ISLAND...AND HIGH PRESSURE CENTERED TO THE DISTANT NW. THIS LAYOUT
IS KEEPING THE LOCAL SURFACE PRESSURE GRADIENT ON THE LOOSE SIDE...
AND IS LEADING TO LIGHT AND VARIABLE WINDS OVER THE E END OF THE
STATE...WITH GENTLE TO LOCALLY MODERATE NE WINDS OVER THE W END.
MIMIC-TPW SATELLITE IMAGERY DEPICTS A LARGE AREA OF HIGH ATMOSPHERIC
MOISTURE CONTENT EXTENDING FAR TO THE ENE OF THE BIG ISLAND...WITH A
TAIL OF ABOVE NORMAL MOISTURE TRAILING TO THE WSW ACROSS MUCH OF THE
STATE. THE 12Z SOUNDINGS SHOWED VERY LITTLE CHANGE DURING THE
PREVIOUS 12 HOURS...WITH INVERSIONS BASED AROUND 8K FEET...AND
SLIGHTLY ABOVE NORMAL PWATS NEAR 1.35 INCHES.

STRONG W/NW WINDS CONTINUE ON THE BIG ISLAND SUMMITS DUE TO A
MID-LEVEL TROUGH TO THE N...WITH THE CFHT SENSOR SHOWING SUSTAINED
WINDS CONSISTENTLY AROUND 50 MPH WITH GUSTS NEAR 60 MPH AT TIMES
DURING THE NIGHT. A WIND ADVISORY REMAINS POSTED FOR THE SUMMITS
THROUGH 6 PM TODAY...AND THE GRADIENT ALOFT SHOULD WEAKEN
SUFFICIENTLY BY THAT TIME TO ALLOW THE ADVISORY TO EXPIRE.

TODAY SHOULD BE SIMILAR TO THURSDAY...WITH NE BACKGROUND FLOW AND
LOCALIZED SEA BREEZES OVER THE W ISLANDS...AND LIGHT FLOW WITH MORE
WIDESPREAD SEA BREEZES OVER THE EASTERN ISLANDS. AREAS OF ABOVE
NORMAL MOISTURE LINGERING AROUND THE STATE MAY PRODUCE MORE
CLOUDINESS AND A BIT MORE SHOWER ACTIVITY THAN WOULD OTHERWISE BE
THE CASE ACROSS INTERIOR AND LEEWARD AREAS ONCE AGAIN THIS AFTERNOON.

LIGHT TO MODERATE TRADES WILL RETURN TO MOST OF THE STATE THIS
WEEKEND...AS HIGH PRESSURE BUILDS TO THE NW. GUIDANCE HAS TRENDED
STRONGER WITH THE TRADE WIND FLOW ACROSS THE SMALLER ISLANDS ON
SATURDAY...PARTICULARLY KAUAI/OAHU...WITH LIGHTER WINDS AROUND
THE BIG ISLAND AS THE SURFACE TROUGH LINGERS TO THE NE. CONTINUED
ABOVE NORMAL MOISTURE AND RELATIVELY WEAK INVERSIONS SHOULD ALLOW
FOR ACTIVE TRADE SHOWERS ACROSS WINDWARD AND MAUKA AREAS. SEA
BREEZES ON THE SMALLER ISLANDS WILL MAY BE LIMITED DUE TO THE
EXPECTED STRONGER TRADES...BUT WITH THE EXTRA MOISTURE IN PLACE WE
COULD STILL SEE ISOLATED TO WIDELY SCATTERED AFTERNOON SHOWERS
DEVELOP ACROSS SOME INTERIOR/LEEWARD AREAS...ESPECIALLY ON MAUI. THE
KONA COAST OF THE BIG ISLAND SHOULD SEE SOMEWHAT BETTER RAIN
CHANCES...AS IS OFTEN THE CASE DURING THE SUMMER MONTHS.

TRADES MAY WEAKEN SLIGHTLY EARLY NEXT WEEK AS THE SFC HIGH SHIFTS
NE...AND THE SURFACE TROUGH NE OF THE BIG ISLAND SHIFTS WESTWARD
OVER THE OTHER ISLANDS. IT MAY BRIEFLY SHARPEN IN RESPONSE TO A
PROGRESSIVE MID-LEVEL TROUGH PASSING FROM W TO E ACROSS THE AREA.
THIS COMBINED WITH CONTINUED ABOVE NORMAL MOISTURE COULD RESULT IN
ENHANCED SHOWERS...BOTH IN THE TYPICAL WINDWARD/MAUKA AREAS...AS
WELL AS OVER INTERIOR/LEEWARD AREAS ALONG LOCAL SEA BREEZES DURING
THE AFTERNOONS. LATEST MODEL GUIDANCE INDICATES A FAIRLY SEASONABLE
TRADE WIND PATTERN FOR THE MIDDLE AND LATTER PART OF THE NEXT
WEEK...WITH LIGHT TO MODERATE TRADE WINDS.

&&

.AVIATION...
OVERNIGHT LAND BREEZES CLEARED OUT MOST ISLAND AREAS LAST NIGHT.
LIGHT TRADE WIND FLOW WILL ALLOW FOR LOCALIZED SEA BREEZES TO SET UP
AND INTERIOR CLOUDS AND SHOWERS TO BUILD THIS AFTERNOON. SOME
SHOWERS MAY INTRODUCE FLEETING PERIODS OF MVFR. NO AIRMETS ARE
EXPECTED THROUGH THE AFTERNOON.

AN AREA OF ENHANCED MOISTURE IS APPROXIMATELY 250 MILES NE OF THE
SMALLER ISLANDS AND IS FORECAST TO BE NEAR THE ISLANDS BY SATURDAY
MORNING. DURING THAT TIME...CLOUDS AND SHOWERS WILL FOCUS OVER
WINDWARD AND MOUNTAIN AREAS AND MOUNTAIN OBSCURATIONS MAY COME INTO
EFFECT.

&&

.MARINE...
A RELATIVELY SMALL LONG-PERIOD S SWELL WILL PERSIST THROUGH
SATURDAY...WITH SURF BELOW ADVISORY LEVELS. A LONGER-PERIOD SSW
SWELL EXPECTED SUNDAY IS LIKELY TO PRODUCE ADVISORY-LEVEL SURF ALONG
S FACING SHORES INTO TUESDAY...WITH PEAK OPEN OCEAN SWELL HEIGHTS
NEAR 5 FEET. THIS SWELL MAY CAUSE SURGES IN HARBORS EXPOSED TO THE
S...AND BREAKING WAVES IN AND NEAR S-FACING CHANNEL ENTRANCES.
MARINERS AND BEACHGOERS SHOULD BE ALERT TO THE FACT THAT THIS IS
LIKELY TO BE THE LARGEST S SWELL OF THE SEASON THUS FAR.
OTHERWISE...SMALL AND RELATIVELY SHORT-PERIOD WNW SWELLS WILL
ARRIVE OVER THE NEXT COUPLE OF DAYS...SUPPORTING SMALL SURF ALONG N
FACING SHORES. WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL
CRAFT ADVISORY /SCA/ LEVELS THROUGH THE WEEKEND...AND INTO EARLY
NEXT WEEK...AFTER WHICH STRONGER TRADE WINDS MAY NECESSITATE A SCA
ISSUANCE.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY UNTIL 6 PM HST THIS EVENING FOR BIG ISLAND SUMMITS.

&&

$$

DISCUSSION/MARINE...BIRCHARD
AVIATION...EATON



Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office