High Surf in Hawaii, April 7, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST TUE APR 7 2009

.SYNOPSIS...
TRADE WINDS WILL REMAIN BREEZY THIS WEEK...AS HIGH PRESSURE REMAINS
NORTH OF THE ISLANDS. THE TRADES WILL FOCUS SHOWERS ON WINDWARD
SLOPES. HIGH CLOUDS WILL INCREASE LATE TODAY AND PERSIST THROUGH
THE WEEK.

&&

.DISCUSSION...
A SURFACE HIGH PARKED TO OUR NORTH IS BIG ENOUGH AND THE PRESSURE
GRADIENT STEEP ENOUGH TO PUT MODERATE LOCALLY STRONG TRADES OVERHEAD
THROUGH THE WORKWEEK. THE HIGH WILL SHIFT EASTWARD TO WELL NORTHEAST
OF THE ISLANDS...LEADING TO A RELAXATION OF THE PRESSURE GRADIENT
AND THUS THE TRADES OVER THE WEEKEND.

THERE IS A BROAD UPPER LEVEL TROUGH RUNNING NORTHEAST TO SOUTHWEST
JUST NORTH OF THE STATE. WATER VAPOR SATELLITE IMAGERY DOES NOT SHOW
ANY SMALLER SHORTWAVE TROUGH SWINGING THROUGH THE LARGER LONGWAVE
TROUGH...WHICH IS SOMETHING WE LOOK FOR FOR SHOWER ENHANCEMENT.
MODELS SAY THAT SUCH A SHOWER-MAKING SHORTWAVE TROUGH SHOULD NOT
OCCUR THIS WEEK. TEMPERATURES ALOFT ASSOCIATED WITH THE UPPER LOW
ARE COLD...-12C TO -14C...BUT THEY DO NOT APPEAR TO BE COLD ENOUGH
TO CAUSE AN ENHANCEMENT OF THE TRADE SHOWERS. TEMPERATURES ALOFT ARE
NOT EXPECTED TO GET ANY COLDER...AND IN FACT WILL LIKELY GET WARMER.
SO THE AIRMASS IS NOT EXPECTED TO BECOME MORE UNSTABLE AND THE
SHOWERS HEAVIER THAN THEY ALREADY ARE.

THE TROUGH APPEARS TO BE DECOUPLED FROM THE TRADE REGIME BELOW BY A
SOMEWHAT STRONG SUBSIDENCE INVERSION OF SEVERAL DEGREES C BETWEEN 7
AND 9 THOUSAND FEET. INFRARED SATELLITE IMAGERY SHOWS NO SIGNIFICANT
ENHANCEMENT IN THE LOW CLOUD FIELD OVER AND UPSTREAM OF THE ISLANDS
...CONFIRMING THE GOOD JOB THAT THE INVERSION IS DOING IN CAPPING
THE LOW CLOUDS. MODELS DO NOT SHOW ANY SUBSTANTIAL WEAKENING OF THE
INVERSION WHICH WOULD LEAD TO ENHANCED SHOWERS...ALTHOUGH THERE MAY
BE AN INCREASE IN SHOWERS COME THURSDAY THANKS TO POSSIBLE MOISTURE
SPREADING NORTHWARD OVER THE STATE. SO...IT LOOKS LIKE ABOUT THE
ONLY THING THE UPPER TROPOSPHERIC TROUGH WILL DO IS DRAG UP A LOT OF
MID AND HIGH CLOUDS FROM THE SOUTHWEST...STARTING LATE TODAY OR
TONIGHT.

&&

.MARINE...
A NORTHWEST SWELL IS ON ITS WAY AND A HIGH SURF ADVISORY IS UP FOR
RISING SURF ALONG NORTH AND SELECT WEST FACING SHORES. SURF HEIGHTS
SHOULD BE NEAR 15 FT BY SUNUP...AND COULD PEAK NEAR 20 FT LATER
TODAY. A GRADUAL DECREASE WILL FOLLOW THROUGH THE REST OF THE WORK
WEEK. IT DOES NOT LOOK LIKE THE SWELL WILL CAUSE ANY PROBLEMS ALONG
THE KONA SIDE...AS THAT COAST WILL PROBABLY FALL IN THE SWELL SHADOW
OF THE SMALLER ISLANDS.

A SMALL CRAFT ADVISORY CONTINUES THROUGH TONIGHT FOR ALL WATERS.
EACH MARINE ZONE IS EXPECTED TO HAVE AT LEAST A PORTION EXPOSED TO
COMBINED SEAS GREATER THAN 10 FEET AND WINDS IN THE 25 KT RANGE.
WITH THE HIGH NORTH OF THE ISLANDS AROUND 1030 MB...THE ADVISORY FOR
THE NORMALLY WINDY AREAS WILL LIKELY BE IN PLACE FOR MOST OF THE
WEEK.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM TODAY FOR NORTH AND WEST FACING SHORES
OF NIIHAU...KAUAI...OAHU AND MOLOKAI...AND FOR NORTH FACING SHORES
OF MAUI.

SMALL CRAFT ADVISORY THROUGH TONIGHT FOR ALL HAWAIIAN WATERS...AND
FOR MAALAEA BAY...WATERS SOUTH OF THE BIG ISLAND...AND THE PAILOLO
AND ALENUIHAHA CHANNELS UNTIL FRIDAY MORNING.

&&

CRAIG