Small Craft Advisory 73, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST THU APR 4 2013

.SYNOPSIS...
LIGHT TRADE WINDS WILL CONTINUE THROUGH TONIGHT...THEN INCREASE
ON FRIDAY AND SATURDAY. WINDS WILL TURN SOUTHEAST AND WEAKEN AGAIN
EARLY NEXT WEEK. BRIEF SHOWERS WILL FAVOR WINDWARD AREAS MAINLY
DURING THE NIGHT AND EARLY MORNING. LIGHT WINDS TODAY WILL ALLOW
CLOUDS AND ISOLATED SHOWERS TO DEVELOP OVER LEEWARD AND INTERIOR
AREAS DURING AFTERNOON. A LARGE NORTHWEST SWELL BUILDING THROUGH
TONIGHT WILL BRING HAZARDOUS SURF TO NORTH AND WEST FACING SHORES
THROUGH FRIDAY NIGHT.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS NEARLY ZONAL FLOW WITH A BROAD RIDGE JUST
WEST OF THE STATE...BETWEEN A BROAD TROUGH TO THE EAST AND A WEAK
TROUGH WELL TO THE WEST. A 90KT WESTERLY UPPER LEVEL JET IS LOCATED
JUST SOUTH OF THE STATE. AT THE SURFACE...A RIDGE IS LOCATED OVER
THE NORTHERN OFFSHORE WATERS...ASSOCIATED WITH A WEAK HIGH FAR EAST
NORTHEAST OF THE STATE. 12Z SOUNDINGS FROM LIHUE AND HILO SHOW
INVERSIONS AROUND 7-8KFT...WITH PRECIPITABLE WATERS RANGING FROM
0.94 INCHES AT HILO TO 1.16 INCHES AT HILO. EARLY MORNING MIMIC
TOTAL PRECIPITABLE WATER IMAGERY SHOWS HIGHER MOISTURE EXTENDING
EAST OF THE BIG ISLAND.

THE LIGHT PRESSURE GRADIENT WITH THE RIDGE JUST NORTH OF THE STATE
ALLOWED LAND BREEZES TO DEVELOP OVERNIGHT...AND SEA BREEZES ARE
EXPECTED FOR LEEWARD SECTIONS TODAY. IN THIS TYPE OF PATTERN...
CLOUDS AND SHOWERS DEVELOP ACROSS INTERIOR/LEEWARD SECTIONS DURING
THE AFTERNOON WHILE WINDWARD CLOUDS TYPICALLY DIMINISH OR CLEAR OUT
ALTOGETHER. THE CURRENT FORECAST HAS THIS IN HAND...WITH MOSTLY
CLOUDY CONDITIONS ACROSS LEEWARD SECTIONS BY AFTERNOON. LAND BREEZES
WILL DEVELOP AGAIN TONIGHT ACROSS LEEWARD SECTION. TRADE WINDS WILL
BE SLIGHTLY STRONGER TONIGHT THAN LAST NIGHT...AND DEWPOINT ARE A
FEW DEGREES WARMER. THEREFORE...LOW TEMPERATURES ARE EXPECTED TO BE
A COUPLE DEGREES WARMER THAN LAST NIGHT.

ON FRIDAY AND SATURDAY...THE HIGH NORTHEAST OF THE STATE STRENGTHENS
TO NEAR 1030MB AND REMAINS NEARLY STATIONARY. TRADE WINDS OVER THE
STATE WILL RESPOND BY INCREASING TO MODERATE TO FRESH SPEEDS
FRIDAY...AND REMAINING THAT WAY THROUGH SATURDAY. GIVEN THE LOCATION
OF THE LOW...THE TRADE WIND DIRECTION WILL BE MORE DUE EASTERLY THAN
IS TYPICAL. FORECAST SOUNDINGS AND CROSS SECTIONS SHOW LOW
INVERSIONS AND LIMITED LOW-LEVEL MOISTURE...WITH SLIGHTLY HIGHER
VALUES OVER THE EASTERN HALF OF THE STATE. THE INCREASED TRADES WILL
FOCUS THE LIMITED MOISTURE OVER WINDWARD SLOPES...WITH BRIEF SHOWERS
FAVORING NIGHTS AND MORNINGS.

FOR SUNDAY INTO EARLY NEXT WEEK...THE SURFACE HIGH SLOWLY DRIFTS
EASTWARD AS A FRONT APPROACHES FROM THE WEST. THERE ARE DIFFERENCES
BETWEEN THE GFS/ECMWF/NAVGEM WITH RESPECT TO THE LOW THAT DEVELOPS
AND TRACKS NORTH OF THE STATE. THE 12Z GFS AND ECMWF ARE IN BETTER
AGREEMENT THAN EARLIER RUNS...BUT THE ECMWF IS STILL SLOWER AND
STRONGER AS THE SYSTEM TRACKS NORTHEASTWARD. CLOSER TO THE
ISLANDS...THE GFS IS STRONGER THAN THE ECMWF WITH THE FRONT THAT
MOVES IN FROM THE NORTHWEST...WHICH DOES NOT SEEM AS LIKELY GIVEN
THE UPPER LEVEL PATTERN WITH ENERGY STAYING WELL NORTH OF THE AREA.
EVEN THE WEAKER BOUNDARY WILL DISPLACE THE RIDGE SOUTHWARD...AND
CAUSE WINDS TO VEER TO THE EAST-SOUTHEAST. WHILE THE GRADIENT MAY
MAINTAIN ITS STRENGTH...THE SMALLER ISLANDS MAY BE BLOCKED BY THE
BIG ISLAND AND CONSEQUENTLY SEE LIGHTER WINDS WITH LOCAL LAND AND
SEA BREEZE CIRCULATIONS. CONDITIONS SHOULD REMAIN DRY AND STABLE...
LEADING TO RAINFALL CHANCES WELL BELOW NORMAL FROM SUNDAY INTO
MONDAY.

BY THE MIDDLE OF THE WEEK...LOCAL DIFFERENCES BETWEEN THE GFS AND
ECMWF CONTINUE TO INCREASE. THE GFS HOLDS ONTO THE FRONT THAT IS
STALLED JUST OUTSIDE OF THE OFFSHORE WATERS...LIFTING IT NORTHWARD
SLOWLY AND KEEPING SOUTHEASTERLY FLOW ACROSS THE ISLANDS FOR LONGER.
THE ECMWF...WHICH WAS NOT AS STRONG WITH THE FRONT INITIALLY...
WEAKENS IT FURTHER AND LIFTS IT NORTHWARD FASTER THAN THE GFS. THIS
RETURNS MORE TYPICAL TRADE WINDS TO THE ISLANDS. IN ADDITION TO THE
EARLIER PREFERENCE TOWARD THE ECMWF SOLUTION...IT IS ALSO MORE IN
LINE WITH CLIMATOLOGY. THE CURRENT FORECAST IS GEARED MORE TOWARD
THE ECMWF SOLUTION.

&&

.AVIATION...
VFR CONDITIONS WILL PREVAIL AT ALL TERMINALS THROUGH 18Z FRIDAY.
ISOLATED MVFR WILL BE POSSIBLE THIS AFTERNOON OVER MOUNTAIN AND
INTERIOR SECTIONS OF THE ISLANDS AS SEA BREEZES ARE EXPECTED.

&&

.MARINE...
A POWERFUL NORTHWEST SWELL REACHED BUOY 51101 NW OF KAUAI
OVERNIGHT...AND CONTINUES TO BUILD THIS MORNING. LONG-PERIOD
FORERUNNERS ALSO REACHED THE WAIMEA BUOY EARLY THIS MORNING.
LIFEGUARDS ON KAUAI REPORTED SURF UP TO 25 FEET...AND WE HAVE
UPGRADE THE HIGH SURF ADVISORY TO A WARNING. SURF WILL CONTINUE TO
BUILD ACROSS THE REST OF THE STATE THIS AFTERNOON AND EVENING. WITH
THE SWELL AT BUOY 51101 STILL ON ITS WAY UP...THE PEAK SHOULD ARRIVE
TONIGHT...WHICH IS IN LINE WITH THE 12Z WAVEWATCH III GUIDANCE.

COMBINED SEAS ARE EXPECTED TO EXCEED 10 FEET TONIGHT THROUGH FRIDAY
NIGHT...PRIMARILY DUE TO THE NORTHWEST SWELL. THIS WILL NECESSITATE
THE ISSUANCE OF A SMALL CRAFT ADVISORY /SCA/ THIS AFTERNOON FOR MOST
COASTAL WATERS. INCREASING TRADE WINDS MAY EXCEED 25 KT IN THE
WINDIER MARINE ZONES AROUND MAUI AND THE BIG ISLAND THIS WEEKEND...
WHICH WOULD ALSO REQUIRE THE ISSUANCE OF AN SCA.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF WARNING UNTIL 6 AM HST SATURDAY FOR NORTH AND WEST FACING
SHORES OF NIIHAU KAUAI OAHU AND MOLOKAI AND NORTH FACING SHORES OF
MAUI.

HIGH SURF ADVISORY UNTIL 6 AM HST SATURDAY FOR WEST FACING SHORES
OF MAUI.

&&

PUBLIC/MARINE...BRAVENDER
AVIATION...EVANS/BURKE