High Wind in Hawaii, March 31, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST SUN MAR 31 2013

.SYNOPSIS...
THE COLD FRONT NEAR THE BIG ISLAND WILL SLOWLY DISSIPATE TODAY.
WHILE A PASSING PERIOD OF SHOWERS MAY OCCUR LATE TONIGHT THROUGH
MONDAY NIGHT...THE GENERAL TREND IS TOWARD COOLER AND DRIER
CONDITIONS AS NORTHERLY POST-FRONTAL WINDS SPREAD OVER THE ISLANDS.
THESE NORTHERLY WINDS WILL GRADUALLY VEER AND BECOME EAST TO
NORTHEAST TRADES BY THURSDAY...STRENGTHENING FROM LIGHT TO MODERATE
BY THE WEEKEND.

&&

.DISCUSSION...
SATELLITE LOOP SHOWS DRY NORTHERLY FLOW SPREADING SOUTHWARD ACROSS
THE ISLANDS AS AN OLD FRONTAL BOUNDARY NEAR THE BIG ISLAND BEGINS TO
DISSIPATE. MORNING SOUNDINGS SHOW A SHARP TEXTBOOK CONTRAST IN AIR
MASSES BETWEEN PRE-FRONTAL HILO AND POST-FRONTAL LIHUE. HILO WAS
MOIST AND UNSTABLE WITH OVER 1.4 INCHES OF PRECIPITABLE WATER...NO
INVERSION AND A K-INDEX VALUE OF PLUS 34. LIHUE WAS DRY AND STABLE
WITH ABOUT 0.5 INCHES OF PRECIPITABLE WATER...A STRONG INVERSION
NEAR 4600 FEET AND A K-INDEX VALUE OF MINUS 14. LAYERED CLOUDS
MARKING THE FRONTAL BOUNDARY PERSIST ACROSS PORTIONS OF THE BIG
ISLAND AND ACROSS ADJACENT WINDWARD WATERS...BUT SATELLITE LOOP AND
RADAR SHOW THAT NORTHERLY FLOW HAS NOT ONLY REACHED THE BIG ISLAND
BUT HAS ACTUALLY PUSHED ACROSS WATERS SOUTHEAST OF THAT ISLAND THIS
MORNING. THE STABLE WARM-TOPPED LOW CLOUDS EMBEDDED IN THE NORTHERLY
POST FRONTAL FLOW AROUND THE SMALLER ISLANDS ARE PRODUCING LITTLE OR
NO PRECIPITATION. WE EXPECT DRY AND CLEARING CONDITIONS ACROSS MOST
OF THE SMALLER ISLANDS TODAY...WHILE MORE GENEROUS CLOUD COVER WILL
LIKELY LINGER ACROSS NORTH-FACING MAUI SLOPES INTO THIS AFTERNOON.
CLEARING IS EXPECTED ACROSS NORTH AND EAST FACING BIG ISLAND SLOPES
BY TONIGHT.

THE LOW ASSOCIATED WITH THE OLD FRONTAL BOUNDARY IS CENTERED ABOUT
940 MILES NORTH OF THE ISLANDS NEAR 35N155W. THIS LOW IS SLOW-MOVING
AND QUITE STRONG...GENERATING GALE FORCE WINDS ACROSS POTIONS OF OUR
HIGH SEAS AREA OF RESPONSIBILITY BUT FAR NORTH OF LOCAL WATERS.
THESE STRONG WINDS AROUND THE LOW HAVE GENERATED A SWELL WHICH IS
PRODUCING ADVISORY LEVEL SURF ACROSS EXPOSED LOCAL SHORES. THE
JETSTREAM ASSOCIATED WITH THE SUPPORTING UPPER TROUGH WILL KEEP
WINDS ABOVE HIGH WIND WARNING THRESHOLD AT THE BIG ISLAND SUMMITS
THROUGH TONIGHT AND INTO MONDAY MORNING.

GFS AND ECMWF SHOW A SECOND...BUT WEAKER...BOUT OF SHOWERS WILL
REACH THE ISLANDS FROM THE NORTH LATE TONIGHT THROUGH MONDAY NIGHT
AS A POST-FRONTAL IMPULSE WRAPS AROUND THE LOW. WE EXPECT ANY
SHOWERS WITH THIS IMPULSE TO PASS QUICKLY SOUTHEASTWARD WITHIN
CONTINUED NORTHERLY FLOW AND MOVE EAST OF THE MAIN ISLAND CHAIN
TUESDAY AFTERNOON. A SURFACE RIDGE WILL NOSE EASTWARD TO THE NORTH
OF THE ISLANDS AFTER THAT. THE GENERAL TREND THROUGH THE FORECAST
PERIOD WILL BE COOL NORTHERLY FLOW GRADUALLY VEERING TO EAST
NORTHEAST TRADE WINDS BY THURSDAY...WITH WIND SPEEDS INCREASING INTO
THE MODERATE RANGE BY NEXT WEEKEND.

&&

.AVIATION...
A STRONG JET STREAM ALOFT ABV FL300 WILL PRODUCE MODERATE CLEAR-AIR
TURBULENCE OVER THE ISLANDS. OTHERWISE...VFR CONDITIONS ARE
EXPECTED TO PREVAIL TODAY.

&&

.MARINE...
A SMALL CRAFT ADVISORY IS IN EFFECT FOR ALL LOCAL WATERS AND
CHANNELS WEST OF MOLOKAI EITHER DUE TO STRENGTHENING WINDS...HIGH
COMBINED SEAS OR A COMBINATION OF BOTH. THIS ADVISORY WILL REMAIN IN
EFFECT UNTIL 6 PM HST MONDAY.

A NORTHWEST SWELL WILL PRODUCE ADVISORY LEVEL SURF ALONG NORTH AND
WEST FACING SHORES OF KAUAI AND NIIHAU...AND ALONG NORTH FACING
SHORES OF OAHU MOLOKAI AND MAUI THROUGH TONIGHT.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY THROUGH 6 AM HST MONDAY FOR NORTH AND WEST FACING
SHORES OF KAUAI AND NIIHAU...AND NORTH FACING SHORES OF OAHU MOLOKAI
AND MAUI.

SMALL CRAFT ADVISORY UNTIL 6 PM HST MONDAY FOR WATERS WEST OF
MOLOKAI.

HIGH WIND WARNING FOR BIG ISLAND SUMMITS UNTIL 9 AM HST MONDAY.

&&

POWELL