Flash Flood Warning 20, NWS Honolulu, HI

588 
WGHW70 PHFO 031455
FFSHFO

FLASH FLOOD STATEMENT
NATIONAL WEATHER SERVICE HONOLULU HI
455 AM HST TUE MAY 3 2011

HIC007-031504-
/O.EXP.PHFO.FF.W.0020.000000T0000Z-110503T1500Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
KAUAI COUNTY-
455 AM HST TUE MAY 3 2011

...THE FLASH FLOOD WARNING HAS EXPIRED FOR THE ISLAND OF KAUAI
COUNTY...

WEATHER RADAR AND RAIN GAGES SHOWED THAT THE HEAVY RAINS ARE 
TAPERING OFF. THUS THE FLASH FLOOD WARNING IS ALLOWED TO EXPIRE.

RUNOFF IS STILL OCCURRING AND STREAMS WILL REMAIN HIGH FOR SEVERAL 
HOURS.

LAT...LON 2241 15949 2169 15917 2154 15960 2226 15992

$$
DONALDSON

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST TUE MAY 3 2011

.SYNOPSIS...
A LOW ALOFT NEAR THE ISLANDS WILL GRADUALLY WEAKEN...MAKING THE
ATMOSPHERE MORE STABLE BY WEDNESDAY. MEANWHILE...A SURFACE HIGH FAR
NORTHEAST OF THE AREA WILL BUILD SOUTHWEST. THE HIGH WILL PRODUCE
LOCALLY BREEZY TRADE WINDS TONIGHT INTO THE WEEKEND. THE TRADE WINDS
WILL WEAKEN EARLY NEXT WEEK AS THE HIGH MOVES AWAY AGAIN.

&&

.DISCUSSION...
A TROUGH ALOFT CONTINUES TO PRODUCE UNSETTLED WEATHER OVER THE MAIN
HAWAIIAN ISLANDS. WATER VAPOR IMAGERY APPEARS TO SHOW ONE LOW ALOFT
ABOUT 400 MILES EAST NORTHEAST OF HILO NEAR 23N150W AND POSSIBLY
ANOTHER LOW 200 MILES WEST OF LIHUE NEAR 22N162W. THE TROUGH OVER
THE AREA IS KEEPING THE ATMOSPHERE VERY UNSTABLE. THE 200 AM BALLOON
SOUNDING AT LIHUE SHOWED A LIFTED INDEX...LI...OF -7.0 AND A CAPE OF
3166 J/KG. THIS IS ABOUT AS UNSTABLE AS IT EVER GETS OVER THE
ISLANDS. AS OF 300 AM...RADARS WERE SHOWING NO HEAVY SHOWERS OVER
THE ISLANDS...BUT THERE WERE SCATTERED MODERATE SHOWERS OVER
WINDWARD AREAS OF OAHU...MAUI AND THE BIG ISLAND AND THERE WERE
SCATTERED HEAVY SHOWERS AND THUNDERSTORMS OVER WATER AROUND THE
ISLANDS FROM MAUI TO OAHU. THE RELATIVE HUMIDITY AT MAUNA KEA SUMMIT
WAS 100 PERCENT WITH TEMPERATURES WELL BELOW FREEZING SO THERE IS
PROBABLY FREEZING FOG ON THE SUMMITS.

THE TROUGH ALOFT IS NEARLY STATIONARY SO THE ATMOSPHERE WILL REMAIN
UNSTABLE ENOUGH FOR MORE THUNDERSTORMS THROUGH THIS EVENING. THE
TROUGH WILL ALSO KEEP TEMPERATURES ALOFT COLD ENOUGH TO CONTINUE THE
POSSIBILITY OF MORE SNOW ON THE BIG ISLAND SUMMITS SO WE HAVE
EXTENDED THE WINTER WEATHER ADVISORY THROUGH WEDNESDAY MORNING. THE
GFS MODEL SHOWS THE TROUGH ALOFT SLOWLY WEAKENING AND SHIFTING
SOUTHEAST OVER THE NEXT 48 HOURS. AS IT DOES...THE ATMOSPHERE OVER
THE ISLANDS WILL SLOWLY BECOME LESS UNSTABLE. SURFACE ANALYSES SHOW
A RATHER STRONG 1035 MB HIGH ABOUT 2200 MILES NORTHEAST OF HONOLULU
NEAR 43N132W. THE HIGH WILL BUILD SOUTHWEST THROUGH SATURDAY. THE
PRESSURE GRADIENT OVER THE MAIN HAWAIIAN ISLANDS WILL TIGHTEN
RAPIDLY TODAY...AND THE TRADE WINDS BECOMING LOCALLY BREEZY BY
TONIGHT. THE COMBINATION OF INCREASING STABILITY AND STRONGER TRADE
WINDS SHOULD END THE THREAT OF THUNDERSTORMS BY LATE TONIGHT.

THE LATEST GLOBAL MODELS CONTINUE TO SHOW THE TROUGH OVER THE MAIN
HAWAIIAN ISLANDS BECOMING PART OF AN EAST TO WEST TROUGH...THE KIND
OFTEN CALLED A TUTT...TROPICAL UPPER TROPOSPHERIC TROUGH. THERE WILL
BE SOME LINGERING INSTABILITY ASSOCIATED WITH THE TUTT...BUT THE
ATMOSPHERE WILL BE LESS UNSTABLE BY MID-WEEK. THE GLOBAL MODELS
CONTINUE TO SUGGEST A LOW ALOFT MAY REDEVELOP NEAR THE ISLANDS BY
THE WEEKEND AND MAKE THE ATMOSPHERE MORE UNSTABLE AGAIN. THE MODELS
ARE STILL RATHER INCONSISTENT...SO IT IS TOO SOON TO KNOW EXACTLY
HOW THIS WILL PLAY OUT.

EARLY NEXT WEEK THE GFS AND ECMWF MODELS ARE SHOWING THE TUTT
BREAKING DOWN AS A DEEP LOW ALOFT DIGS TOWARD THE ISLANDS FROM THE
NORTHWEST. THIS SYSTEM COULD DISRUPT THE TRADES...PRODUCE UNSTABLE
CONDITIONS AND BRING MORE UNSETTLED WEATHER.

&&

.MARINE...
TRADE WINDS WILL LIKELY STRENGTHEN ENOUGH TONIGHT TO REQUIRE A
SMALL CRAFT ADVISORY...SCA...FOR THE WINDIER AREAS AROUND THE BIG
ISLAND AND MAUI AND THE SCA MAY REMAIN UP THROUGH THE WEEK. THE
STRONGER TRADES MAY PRODUCE ROUGH SURF ALONG EAST FACING SHORES...
SO A HIGH SURF ADVISORY COULD BE NEEDED BY MID-WEEK. WE ARE STILL
EXPECTING A MODERATE NORTHWEST SWELL TO PEAK ON THURSDAY AND WE MAY
SEE A MODERATE SOUTH SWELL EARLY NEXT WEEK.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FOR THE SUMMITS OF MAUNA KEA AND MAUNA LOA
THROUGH 900 AM WEDNESDAY.

&&

DONALDSON