Flash Flood in Hawaii, January 26, 2006

HAWAIIAN ISLANDS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST THU JAN 26 2006

.SYNOPSIS...
SHOWERS ENHANCED BY A MID-LEVEL KONA LOW JUST SOUTH OF THE ISLANDS
WILL CONTINUE TO KEEP THE ISLANDS WET FOR THE NEXT 24 TO 36 HOURS.
THE COLD UPPER LOW WILL ALSO BRING MORE SNOW TO THE BIG ISLAND
SUMMITS TODAY...AS IT MOVES SLOWLY EASTWARD. EXPECT THIS LOW TO
CONTINUE ITS EASTWARD MOVEMEMT...GRADUALLY IMPROVING CONDITIONS
OVER THE ISLANDS AND LEADING TO A PLEASANT WEEKEND.

&&

.DISCUSSION...
SATELLITE WATER VAPOR IMAGERY CONFIRMS MODEL TREND OF TAKING WET
UPPER AIR KONA SYSTEM CURRENTLY SOUTH OF THE ISLANDS EASTWARD AND
GRADUALLY DRYING OUT ISLAND WEATHER OVER THE NEXT COUPLE OF DAYS.
MEANWHILE...HEAVY SHOWERS CONTINUE IN THE MOIST ENVIRONMENT
GENERATED BY THE MID-LEVEL LOW PRESSURE SYSTEM TO OUR SOUTH.
FORTUNATELY INDIVIDUAL SHOWERS ARE TENDING TO BE FAIRLY FAST MOVING
IN THE 20,000 FOOT DEEP MOIST LAYER FLOW FROM THE SOUTHEAST. THIS
FLOW AVERAGES 20 TO 25 MPH THROUGH THIS DEEP BOUNDARY LAYER AND
ABSENT ANY SERIOUS TRAINING OF SHOWER BANDS OVER A SINGLE AREA...
THE ISLAND MAY ESCAPE ANY SERIOUS FLASH FLOODING.

WHILE ALL ISLANDS HAVE SEEN PERIODIC HEAVY RAINS...THE ISLAND MOST
AFFECTED BY THE HEAVY RAINFALL HAS BEEN THE BIG ISLAND OF HAWAII.
HERE 24 HOUR RAINFALL TOTALS OF 2 TO OVER 6 INCHES...AT HAKALAU RAIN
GAGE ALONG THE HAMAKUA COAST NORTH OF HILO...HAS CAUSED STREAMS AND
RIVERS ON THE WINDWARD OR EASTERN SLOPES OF THE ISLAND TO RUN HIGH.
HONOLII STREAM NEAR PAPAIKAU AND KAIWIKI...BETWEEN HILO AND
PEPEEKEO...APPEARS TO HAVE CRESTED JUST ABOVE ITS 12 FOOT THRESHOLD
AT 4 AM THIS MORNING AND IS TRENDING DOWNWARD AT THIS HOUR. THIS
DOES NOT...OF COURSE...MEAN THAT THE RAIN HAS STOPPED AND THE
POSSIBILITY OF FURTHER HEAVY RAIN AND EVEN MINOR FLOODING HAS
LESSENED...BUT DOES CONTINUE TO INDICATE THAT THIS KONA SYSTEM...
WHILE KEEPING THE ISLANDS QUITE WET...HAS NOT YET BECOME A SERIOUS
FLOOD THREAT AS YET.

COMPUTER MODELS CONTINUE TO INDICATE A SLOW EASTWARD MOVEMENT OF THE
MID-LEVEL KONA LOW SYSTEM SOUTH OF THE ISLANDS OVER THE NEXT SEVERAL
DAYS. THIS SHOULD ALLOW DRYER AIR FROM THE NORTHEAST TO EVENTUALLY
FILTER INTO THE ISLAND ATMOSPHERE...REPLACING THE MOISTURE LADEN AIR
PRESENTLY IN PLACE HERE. FORECAST FOR TODAY REFLECTS THE ABUNDANT
MOISTURE AND HEAVY SHOWERS CURRENTLY IN OUR VICINITY...BUT GRADUALLY
DRIES THE ISLANDS OUT...WITH BETTER WEATHER FOR THE WEEKEND.

&&

.MARINE...
WHILE THE MEAN WIND FLOW OVER THE ISLANDS CONTINUES TO BE FROM THE
EAST OR EAST-SOUTHEAST AT 20 TO 25 MPH AT THE SURFACE...BLOCKING OF
THE WIND BY THE ISLANDS THEMSELVES IS MAKING FOR LIGHTER WINDS OVER
THE LAND AREAS. WILL KEEP SMALL CRAFT ADVISORIES OVER THE WATERS
HOWEVER DUE TO THE LARGER SCALE WIND FIELD AND SOME ADDITIONAL
CHANNELLING THROUGH THE ISLAND CHANNELS.

THESE FAIRLY STRONG WINDS WILL ALSO KEEP SURF ALONG EAST FACING
SHORES NEAR THE 8 FOOT ADVISORY LEVEL THROUGH SATURDAY. A SMALL
NORTH SWELL WILL ARRIVE EARLY THURSDAY...WITH A LARGE WEST-NORTHWEST
SWELL FOLLOWING CLOSE BEHIND THURSDAY NIGHT AND LIKELY RAISING SURF
ALONG NORTH AND WEST SHORES TO ADVISORY LEVELS OR ABOVE FRIDAY AND
SATURDAY.

&&

.HYDROLOGY...
THE PREVIOUS TEAM DECIDED AGAINST ISSUANCE OF A FLOOD WATCH
OVERNIGHT DESPITE THE HEAVY RAINFALL. AS THE INDIVIDUAL CELLS
PRODUCING THIS HEAVY RAIN CONTINUE TO BE RATHER FAST MOVING...WILL
GO ALONG WITH THIS CALL FOR THE MOMENT. BUT WITH THE ABUNDANT
PRECEDENT MOISTURE...WILL MONITOR THE SITUATION CAREFULLY THROUGH
THE NEXT SEVERAL HOURS. WE CONCUR THAT TODAY WILL BE WET ACROSS
THE STATE WITH ANOTHER 1 TO 3 INCHES OR MORE OF ADDITIONAL RAINFALL
WITH THE HIGHEST AMOUNTS OVER THE ALREADY SATURATED WINDWARD SLOPES
OF THE BIG ISLAND OF HAWAII. FLOOD ADVISORIES ARE ALREADY IN PLACE
IN THIS AREA...BUT FOR THE MOMENT NO FLASH FLOODING IS EXPECTED. WE
WILL CONTINUE TO MONITOR...AND SHOULD HEAVY SHOWERS CONTINUE TO
RAISE STREAM LEVELS...OR PRODUCE EXCESSIVE RAINFALL RATES...
APPROPRIATE FLOOD PRODUCTS WILL BE ISSUED WHERE NEEDED. AT THIS
TIME...THE MAIN PROBLEM APPEARS TO BE MINOR FLOODING OF STREETS AND
ROADWAYS WHERE POOR DRAINAGE HAS ALLOWED WATER TO POND ON ROAD
SURFACES.

SNOWFALL HAS BEEN INTERMITTANT ON THE SUMMITS OF MAUNA KEA AND MAUNA
LOA OVERNIGHT...WITH SOME AREAS RECEIVING A TOTAL OF UP TO ABOUT 5
INCHES. HOWEVER...WITH MUCH OF THIS MELTING AS IT FALLS...SNOW
DEPTHS REMAIN WITHIN THE ADVISORY CATEGORY FOR ACCUMULATIONS.
AGAIN...WILL CONTINUE TO MONITOR THIS SITUATION AND FURTHER
WATCHES...ADVISORIES AND/OR WARNINGS WILL BE ISSUED AS NECESSARY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...

HIGH SURF ADVISORY UNTIL 6 PM HST SATURDAY FOR EAST FACING SHORES OF
KAUAI OAHU MOLOKAI MAUI AND THE BIG ISLAND.

WINTER WEATHER ADVISORY UNTIL 6 PM HST THIS EVENING FOR BIG ISLAND
SUMMITS.

SMALL CRAFT ADVISORY UNTIL 6 PM HST FRIDAY FOR MOST COASTAL WATER
AREAS.
&&

FARRELL