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Hawaiian Islands Synoptic Discussion and Guidance

891
FXHW60 PHFO 260655
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST MON MAY 25 2015

.SYNOPSIS...
COOL AND RELATIVELY DRY NORTHEASTERLY WINDS WILL CONTINUE THROUGH
TUESDAY...WITH WINDS GRADUALLY WEAKENING. LOW CLOUDS AND A FEW LIGHT
SHOWERS CARRIED BY THE WINDS WILL FOCUS ALONG NORTHEAST FACING
SLOPES. FROM TUESDAY INTO NEXT WEEKEND...WINDS ARE EXPECTED TO BE
SUFFICIENTLY LIGHT TO ALLOW LAND AND SEA BREEZES TO PREVAIL...WITH A
SOMEWHAT CLOUDY AND UNSETTLED WEATHER PATTERN EXPECTED.

&&

.DISCUSSION...
AN UNSEASONABLE POST-FRONTAL AIRMASS REMAINS IN PLACE ACROSS THE
STATE TONIGHT...AS GENERAL SYNOPTIC WINDS STAY LIGHT TO LOCALLY
MODERATE OUT OF THE NORTH-NORTHEAST. THIS IS DUE TO A PERSISTENT
SURFACE LOW THAT HOVERED NORTHEAST OF THE ISLANDS IN THE PAST COUPLE
OF DAYS. THE NORTHERLY WINDS ARE ALSO BRINGING STABLE LOW CLOUDS TO
THE STATE...PROVIDING MINIMAL PRECIPITATION TO THE AREA. MUCH OF THE
LOW CLOUDS WILL CONTINUE TO AFFECT THE NORTH FACING AREAS OF THE
ISLANDS. WINDS IN THE ISLAND VICINITY ARE RATHER WEAK...AND WILL
ALLOW LAND BREEZES TO DEVELOP AS THE NIGHT PROGRESSES. USUALLY SKIES
MAY CLEAR OVER THE ISLANDS UNDER THE LAND BREEZE...BUT IN THIS
CASE...THERE MAY BE ENOUGH LOW CLOUDS FROM THE NORTHERLY WIND FLOW
TO KEEP SKIES SOMEWHAT CLOUDY...ESPECIALLY ACROSS THE NORTH FACING
AREAS.

THE AFOREMENTIONED SURFACE LOW WILL LIFT SLIGHTLY MORE NORTH IN THE
COMING DAYS THEN TRACK A LITTLE WEST. AS SUCH...THE PRESSURE
GRADIENT ACROSS THE STATE REMAINS SLACK...RESULTING IN RATHER LIGHT
EASTERLY WINDS PREVAILING ACROSS THE STATE THROUGH REST OF THE WEEK.
WINDS WILL BE LIGHT ENOUGH TO ALLOW DAYTIME SEA BREEZES AND
NIGHTTIME LAND BREEZES TO DEVELOP. THEREFORE...EXPECT A HYBRID LIGHT
TRADE WINDS WITH LOCAL LAND AND SEA BREEZES TYPE WIND SCENARIO FOR
THE ISLANDS THROUGH REST OF THE WEEK. MODEL SOLUTIONS INDICATE THERE
WILL ALSO BE AN UPPER LEVEL LOW PERSISTS FAR NORTH-NORTHEAST OF THE
ISLANDS...WITH SOME WEAK SHORTWAVES RIDING ALONG THE UPPER LEVEL
FLOW...PASSING THROUGH THE ISLANDS. AIR MASS IN THE ISLAND VICINITY
WILL STAY SOMEWHAT STABLE EVEN WITH THE PASSAGES OF THE
SHORTWAVES...AS INDICATED BY THE MODELS. ON THE OTHER HAND...THE LOW
LEVEL MOISTURE MAY DEEPEN A BIT UNDER THE INFLUENCE OF THESE PASSING
SHORTWAVE...RESULTING IN A POSSIBLE INCREASE IN CLOUDS AND SHOWERS
OVER THE ISLANDS...ESPECIALLY IN THE AFTERNOON AND EVENING UNDER
DAYTIME SEA BREEZES.

BY THE NEXT WEEKEND...A WEAK SURFACE HIGH BUILDS NORTH OF THE STATE.
THE SURFACE WEATHER PATTERN REMAINS RATHER COMPLEX TO OUR
NORTH...BUT A SLIGHT STRENGTHENING OF THE PRESSURE GRADIENT IS
EXPECTED OVER THE ISLANDS. SLIGHTLY STRONGER TRADE WINDS ARE
EXPECTED TO THE STATE...THOUGH SYNOPTIC WINDS MAY STILL BE LIGHT
ENOUGH FOR LOCALIZED SEA BREEZES TO DEVELOP ACROSS LEEWARD AREAS.
THEREFORE CLOUDS AND SHOWERS WILL AFFECT THE WINDWARD AREAS AT
NIGHTS AND MORNINGS...WHILE LEEWARD AREAS MAY SEE MORE CLOUDS AND
POSSIBLE SHOWERS DURING THE AFTERNOONS AND EVENINGS.

&&

.AVIATION...
A LIGHT TO MODERATE N TO NE FLOW WILL CONTINUE TO PILE UP MAINLY
STABLE STRATOCUMULUS ACROSS NORTH FACING AND WINDWARD SLOPES.
SCATTERED SHOWERS WILL PREVAIL OVERNIGHT ACROSS THESE SECTIONS OF
OAHU AND KAUAI...WITH ISOLATED SHOWERS AT MOST ELSEWHERE. WITH CLOUD
BASES RUNNING A BIT HIGHER THAN NORMAL...VFR CONDITIONS SHOULD
PREVAIL...WITH VFR CEILINGS SPILLING OVER INTO LEEWARD SECTIONS OF
THE SMALLER ISLANDS...ESPECIALLY ON KAUAI AND OAHU. NO AIRMETS ARE
CURRENTLY EXPECTED OVERNIGHT...ALTHOUGH THERE IS A SMALL CHANCE THAT
AIRMET SIERRA FOR MOUNTAIN OBSCURATION COULD BE NEEDED ON
WINDWARD/NORTH SECTIONS OF OAHU AND/OR KAUAI.

VFR CONDITIONS WILL CONTINUE TO PREVAIL ON TUESDAY. LIGHT N/NE
BACKGROUND FLOW WILL ALLOW FOR WIDESPREAD SEABREEZES TO DEVELOP BY
AFTERNOON. CLOUDS AND WIDELY SCATTERED SHOWERS WILL DEVELOP ACROSS
INTERIOR AND LEEWARD AREAS...BUT ONLY ISOLATED MVFR CONDITIONS ARE
EXPECTED.

&&

.MARINE...
SMALL CRAFT ADVISORY LEVEL WINDS OR SEAS ARE NOT EXPECTED THROUGH
THE WEEK...AS WINDS IN THE ISLAND VICINITY REMAIN LIGHT TO
MODERATE...WHILE SWELLS FROM THE S...SSW...NNE...AND WNW ARE MODEST
AT MOST.

SURF WILL REMAIN ELEVATED AND JUST BELOW ADVISORY LEVEL ALONG SOUTH
FACING SHORES THROUGH THE NEXT COUPLE OF DAYS...AS THE CURRENT SOUTH
SWELL PEAKS THROUGH EARLY TUESDAY...THEN SLOWLY SUBSIDE THROUGH
THURSDAY. LATEST SURFACE ANALYSES AND WAVE WATCH MODEL OUTPUT
INDICATE THAT A NEAR-STORM FORCE LOW NOW BREWING EAST OF NEW ZEALAND
IS PRODUCING A SWELL THAT WILL ARRIVE NEXT WEEKEND...WITH INITIAL
INDICATIONS THAT THIS SWELL WILL BRING NEAR ADVISORY LEVELS SURF FOR
SOUTH FACING SHORES.

&&

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

&&

$$

DISCUSSION/MARINE...HUI
AVIATION...JACOBSON



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