Flash Flood Warning 11, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 AM HST THU JUL 23 2009

.SYNOPSIS...
A WESTWARD MOVING SURFACE TROUGH OF LOW PRESSURE WILL BRING LIGHTER
TRADE WINDS AND AN INCREASE IN SHOWERS TO MANY OF ISLANDS THROUGH
FRIDAY. A MORE TYPICAL TRADE WIND WEATHER SCENARIO WILL RETURN BY
MONDAY OF NEXT WEEK.

&&

.DISCUSSION...
ALL INDICATIONS POINTS TO A SUBTLE SURFACE OR LOW LEVEL TROUGH
ORIENTED NORTHEAST TO SOUTHWEST ACROSS OR IN THE VICINITY OF OAHU
THIS EARLY THURSDAY MORNING. THIS TROUGH IS SLATED BY THE GFS MODEL
TO PUSH WEST OF KAUAI COUNTY EARLY THIS EVENING. IN ITS WAKE....A
SLIGHT SOUTH OF EAST WIND COMPONENT WILL SETTLE OVER THE ISLANDS.
AND UNDER THIS PREVAILING WIND DIRECTION...THE SHELTERED WIND AREAS
WILL ENCOUNTER SEA BREEZES DURING THE DAY...THE NIGHT TIME HOURS
WILL HAVE OFFSHORE LAND BREEZES. OVER THE EXPOSED WINDWARD WATERS...
A STIFFER EAST TO SOUTHEAST WIND FLOW WILL BE EVIDENT. THE SOUTHEAST
WIND MAY ALSO SPREAD THE VOG FROM THE BIG ISLAND TO AS FAR AS OAHU.
THE MOST IMPORTANT ISSUE AS WE NEAR THE WEEKEND...IS THAT THE
HUMIDITY WILL BE UP...THE COMFORT LEVEL DOWN.

SHOWER ACTIVITY HAVE PICKED UP HERE AND THERE SINCE 10 PM LAST
EVENING. ANOTHER ROUND OF SCATTERED SHOWERS MOVED ONSHORE OF THE
BIG ISLAND/S PUNA AND KAU COASTS...SCATTERED SHOWERS DEVELOPED OVER
THE LEEWARD WATERS OF MAUI COUNTY WHILE SHOWERS PERSISTED ACROSS THE
THE KOOLAU MOUNTAINS AND ADJACENT AREAS OF OAHU. WINDWARD KAUAI HAD
THE BEST OF THE SHOWERS AS THE LEADING EDGE OF THIS AREA OF TROPICAL
MOISTURE REACH THEM AT AROUND MIDNIGHT. MANY OF THE RAIN GAGES ON
THE WINDWARD SIDE OF KAUAI COLLECTED UP TO 59 HUNDREDTHS OF AN INCH
OF THE WET STUFF DURING A 3 HOUR PERIOD ENDING AT 2 THIS MORNING.

THE CURRENT SHOWERS WILL LIKELY TONE DOWN AS THE MORNING PROGRESSES
THEN REAPPEAR THIS AFTERNOON AS A RESULT OF DAYTIME HEATING AND
LIGHT WINDS. SOME OF THESE SHOWERS HAVE THE POTENTIAL TO BE BRIEFLY
HEAVY THIS AFTERNOON OVER THE INTERIOR SECTIONS OF THE SMALLER
ISLANDS. DO NOT BELIEVE THE AIR MASS IS SUPPORTIVE OF THUNDERSTORMS
OVER LAND AND ADJACENT COASTAL WATERS INCLUDING THE BIG ISLAND THIS
AFTERNOON. THE NAM SOLUTION SUGGESTS ISOLATED THUNDERSTORMS OVER THE
OFFSHORE WATERS TO THE NORTHEAST AND SOUTH OF THE ISLANDS.

THE GFS SUGGEST MID LEVEL RIDGING
TO SLIDE IN THIS EVENING ACROSS THE AREA AND PERSIST THROUGH THE
WEEKEND. THIS RIDGE WILL KEEP THE HEAVY SHOWERS IN CHECK.

WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL LOW AT 28N168W OR ABOUT 670
MILES NORTHWEST OF KAUAI AND ANOTHER AT 31N147W OR 870 NORTHEAST OF
MAUI. A SOUTHWEST WIND FLOW BLOWS HIGH ABOVE THE MAIN HAWAIIAN
ISLANDS. IN THIS WIND FLOW...THERE MAY BE A JETLET OR TWO THAT CAN
INSTIGATE A LOCALLY HEAVY SHOWER BETWEEN NOW AND THIS AFTERNOON.

THE TRADE WINDS ARE EXPECTED TO RETURN IN THE MODERATE RANGE AS
EARLY AS SUNDAY NIGHT.

.MARINE...
ALL WIND SENSORS STATEWIDE HAD A SOFTENING OF THE WINDS. SO THE
SMALL CRAFT ADVISORY FOR THE NORMALLY WINDY MARINE ZONES HAS BEEN
LOWERED.

LOOKS LIKE THE NEW SOUTH SWELL IS MARGINALLY AT ADVISORY LEVEL. WILL
KEEP THE ADVISORY UP THROUGH THIS AFTERNOON/EVENING.

GLOBAL MODELS DEEPEN A STORM LOW SOUTHEAST OF NEW ZEALAND OVER THE
NEXT SEVERAL DAYS. THE INTENSE STORM SHOULD SEND A SOUTH SWELL TO
THE ISLANDS...ARRIVING AROUND AUGUST 1.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 12 PM HST FRIDAY FOR SOUTH FACING SHORES.

&&

H LAU