Heavy Rain in Hawaii, June 6, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 PM HST FRI JUN 6 2014

.SYNOPSIS...
BREEZY TRADE WINDS WILL CONTINUE INTO NEXT WEEK...WITH PASSING
SHOWERS FAVORING WINDWARD AND MAUKA AREAS...ESPECIALLY DURING NIGHTS
AND MORNINGS. SOME OF THE SHOWERS WILL DRIFT LEEWARD ON THE SMALLER
ISLANDS...WHILE THE KONA SLOPES ON THE BIG ISLAND WILL SEE AFTERNOON
AND EVENING SHOWERS.

&&

.DISCUSSION...
CURRENTLY...A 1030 MB SURFACE HIGH CENTERED ABOUT 1675 MILES TO THE
NE IS SUPPLYING MODERATE TO LOCALLY STRONG TRADE WINDS...WITH AN
MORNING ASCAT PASS SHOWING 15 TO 20 KT ENE WINDS OVER NEARBY
WATERS. A SOMEWHAT SHOWERY DAY AFFECTED OAHU AND TO A LESSER EXTENT
KAUAI...WHILE TRADE SHOWERS WERE SLIGHTLY FEWER OVER MAUI COUNTY
AND THE BIG ISLAND. THIS APPEARS TO BE RELATED TO A LOW ALOFT
CURRENTLY CENTERED ABOUT 350 MILES NNW OF KAUAI...MOVING E 10 MPH.
THE PROXIMITY OF THE LOW HAS ERODED THE SUBSIDENCE INVERSION...
DESPITE INITIAL EXPECTATIONS THAT THE LOW WOULD HAVE MINIMAL EFFECT
ON ISLAND WEATHER. AFTERNOON SOUNDINGS SHOW THE BARELY DETECTABLE
INVERSION TO BE BETWEEN 11 AND 14 KFT...WHICH HELPS TO EXPLAIN WHY
ISLAND TERRAIN HAS BEEN RATHER EFFECTIVE IN DRIVING SHOWER
FORMATION...AS THE TRADES FORCE MOIST AIR OVER THE WINDWARD SLOPES.

AS ONE WOULD EXPECT GIVEN THE TIME OF YEAR...BREEZY TRADE WINDS WILL
PREVAIL THROUGH THE FORECAST PERIOD...DRIVEN BY PERSISTENT HIGH
PRESSURE CENTERED TO THE DISTANT NE. MINOR FLUCTUATIONS IN WIND
SPEED/DIRECTION CAN BE EXPECTED...WITH A MINIMA EXPECTED AROUND
TUESDAY...BUT THESE WILL LIKELY BE IMPERCEPTIBLE TO THOSE NOT
INVOLVED IN ACTIVITIES SENSITIVE TO WIND.

THE LOW ALOFT IS FORECAST TO TRACK SLOWLY BUT STEADILY E OVER THE
NEXT COUPLE OF DAYS...AND THEN LINGER SEVERAL HUNDRED MILES NE OF
THE ISLANDS THROUGH MUCH OF NEXT WEEK...WHILE AN ASSOCIATED
TROUGH EXTENDS WSW OVER THE ISLANDS. THIS MEANS THAT THE SUBSIDENCE
INVERSION WILL CONTINUE TO BE WEAKENED/ERODED FOR THE FORESEEABLE
FUTURE. THUS A SOMEWHAT WET TRADE WIND WEATHER PATTERN WILL
CONTINUE...BUT LIKELY NOT AS WET AS OAHU HAS BEEN TODAY...AS THE
INCOMING CLOUD FIELD AND ISLAND TERRAIN FUEL MODERATE SHOWERS. MOST
OF THESE SHOWERS WILL FOCUS OVER WINDWARD AREAS...BUT THEY WILL BE
TALL ENOUGH AND THE WINDS SUFFICIENTLY STRONG FOR A FEW SHOWERS TO
SPREAD TO LEEWARD AREAS OF THE SMALLER ISLANDS. STILL EXPECT TO SEE
A DIURNAL CYCLE OF SHOWERS...WHERE THEY ARE MOST ACTIVE NIGHTS AND
MORNINGS...AND LEAST ACTIVE IN THE AFTERNOONS. HOWEVER...AFTERNOON
CONVECTIVE CLOUDS WILL FORM OVER LEEWARD BIG ISLAND
SLOPES...DROPPING A FEW SHOWERS.

&&

.AVIATION...
AN E TO W ALIGNED HIGH PRESSURE RIDGE ENTRENCHED FAR N OF THE STATE
WILL REMAIN NEARLY STATIONARY THROUGH THE NEXT SEVERAL DAYS.
PERSISTENT TRADE WINDS EXTENDING UP TO NEAR 10K FT CURRENTLY ARE
JUST BELOW SPEEDS CONSIDERED STRONG ENOUGH TO GENERATE SIGNIFICANT
MECHANICAL TURBULENCE ALONG AND JUST LEE OF THE MOUNTAINS. BUT AN
AIRMET FOR MECHANICAL TURBULENCE COULD BE IMPLEMENTED AGAIN SHOULD
THE WINDS STEP UP IN STRENGTH A BIT.

RANDOM LOW LEVEL MOISTURE IN THE WAY OF LOW CLOUDS AND SHOWERS
PASSING THROUGH THE ISLANDS OCCASIONALLY WITHIN THE TRADE WIND FLOW
WILL CREATE SOME MVFR CONDITIONS MAINLY ALONG THE WINDWARD AND
MOUNTAINS SECTIONS. SOME OF THESE MOISTURE SURGES MAY LEAD TO
MOUNTAIN OBSCURATIONS FROM TIME TO TIME. AIRMET SIERRA FOR MOUNTAIN
OBSCURATION MAY BE ISSUED NOW AND AGAIN OVER INTERMITTENT DURATIONS.

&&

.MARINE...
TRADE WINDS WILL REMAIN STRONG ENOUGH OVER THE WINDY AREAS AROUND
MAUI COUNTY AND THE BIG ISLAND TO REQUIRE A SMALL CRAFT ADVISORY...
SCA...THROUGH AT LEAST SATURDAY NIGHT. WINDS MAY SUBSIDE ENOUGH
EARLY NEXT WEEK TO ALLOW THE SCA TO BE BRIEFLY LOWERED BEFORE WINDS
INCREASE AGAIN SHORTLY THEREAFTER.

NO MAJOR SWELLS ARE EXPECTED THROUGH THE MIDDLE OF NEXT WEEK...
ALTHOUGH SMALL SWELLS FROM THE SSW WILL MAINTAIN SEASONABLY-SIZED
SURF ALONG S FACING SHORES FOR AT LEAST THE NEXT SEVERAL DAYS. SURF
IS EXPECTED TO REMAIN BELOW ADVISORY THRESHOLDS ALONG ALL SHORES.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 AM SUNDAY FOR THE PAILOLO AND
ALENUIHAHA CHANNELS...MAALAEA BAY AND WATERS SOUTH OF THE BIG ISLAND.

&&

PUBLIC/MARINE...BIRCHARD
AVIATION...FUJII