Flash Flood Warning 43, NWS Honolulu, HI

970 
WGHW70 PHFO 290112
FFSHFO

FLASH FLOOD STATEMENT
NATIONAL WEATHER SERVICE HONOLULU HI
312 PM HST TUE MAY 28 2013

HIC003-290115-
/O.EXP.PHFO.FF.W.0043.000000T0000Z-130529T0115Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
HONOLULU HI-
312 PM HST TUE MAY 28 2013

...THE FLASH FLOOD WARNING WILL BE ALLOWED TO EXPIRE FOR THE ISLAND 
OF OAHU IN HONOLULU COUNTY...

THE HEAVY RAINS HAVE SHIFTED TO THE NORTHWEST KOOLAU RANGE.  
RAINFALL HAS EASED OVER THE SOUTHEAST KOOLAU RANGE UPSLOPE FROM 
HONOLULU AND MOANALUA.  

RUNOFF LEVELS WILL REMAIN HIGH FOR SEVERAL HOURS IN KALIHI 
STREAM...MOANALUA STREAM AND HALAWA STREAM.  THUS...THE WARNING 
WILL BE REPLACED WITH A FLOOD ADVISORY FOR HONOLULU COUNTY. 



LAT...LON 2175 15797 2147 15779 2131 15778 2141 15797
      2163 15812

$$

KODAMA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
959 AM HST TUE MAY 28 2013

.SYNOPSIS...
A WEAK RIDGE OF HIGH PRESSURE TO OUR NORTH WILL KEEP WINDS ON THE
LIGHTER SIDE THE NEXT FEW DAYS. A NEARBY UPPER LOW WILL HELP TO
ENHANCE SHOWERS NEAR HE ISLANDS TODAY. THE UPPER LOW WILL MOVE
AWAY FROM THE STATE TONIGHT AND WEDNESDAY WITH MORE STABLE AIR
MAKING A RETURN.

&&

.DISCUSSION...
THE ATMOSPHERE NEAR THE ISLANDS IS MORE UNSTABLE THAN USUAL DUE
TO A NEARBY UPPER LOW TO OUR NE. THE LOW LEVEL FLOW HAS VEERED TO
ESE...AND HEAVY DOWNPOURS HAVE BEEN ANCHORED OVER THE KOOLAU
MOUNTAINS. THE HEAVIER SHOWERS OVER THE WINDWARD SLOPES OF
HALEAKALA APPEAR TO BE FINALLY SUBSIDING.

A COMBINATION OF HIGH PRESSURE FAR TO THE NE OF THE STATE AND THE
PROXIMITY OF THE UPPER LOW IS KEEPING THE PRESSURE GRADIENT RATHER
WEAK OVER THE ISLANDS. THIS WILL ALLOW FOR SEA BREEZES TO TAKE
OVER LARGER AREAS ON EACH ISLAND TODAY...AND THUS WE COULD SEE
SOME AFTERNOON BLOWUPS WITH LOCALIZED DOWNPOURS OVER THE INTERIOR
AND SOME LEEWARD SECTIONS THIS AFTERNOON. THIS IDEA IS CERTAINLY
SUPPORTED BY THE NCEP 4 KM WRF-ARW AND WRF-NMM GUIDANCE AS WELL AS
THE UNIVERSITY OF HAWAII WRF MODEL...AND HAVE ADJUSTED OUR FORECAST
TO REFLECT THIS.

A WEAK PRESSURE GRADIENT WILL CONTINUE TO AFFECT THE ISLANDS
THROUGH ABOUT THU. SHOULD SEE SOME CLEARING TAKE PLACE OVERNIGHT
TONIGHT...BUT THE BACKGROUND FLOW MAY BE JUST STRONG ENOUGH TO
KEEP A THREAT FOR SHOWERS OVER SOME WINDWARD SECTIONS TONIGHT.
WILL NEED TO EVALUATE MORE GUIDANCE BEFORE DECIDING ON FORECAST
CHANGES. AT THE SAME TIME...THE UPPER LOW WILL BEGIN MOVING AWAY
FROM THE ISLANDS...WITH MORE STABLE AIR RETURNING. SO EXPECTING A
MORE SETTLED HYBRID WEAK TRADE WIND/CONVECTIVE PATTERN TO TAKE
HOLD FOR WED-FRI.

THE SUBTROPICAL RIDGE TO THE NORTH REESTABLISHES ITSELF SOMEWHAT THIS
WEEKEND AND THE HIGH TO THE NE STRENGTHENS. THIS SHOULD RESULT IN A
BIT OF AN UPTICK IN TRADES OVER THE WEEKEND...BUT CONFIDENCE AT THIS
POINT IS SOMEWHAT LOW.

&&

.AVIATION...
AIRMET SIERRA IS IN EFFECT FOR MTN OBSC OVER WINDWARD AND MAUKA
AREAS OF OAHU MOLOKAI AND MAUI DUE TO MVFR CIGS AND SHRA. AMPLE
MOISTURE HAS COMBINED WITH WEAK FLOW AND INSTABILITY TO CAUSE AREAS
OF MTN OBSC. ELSEWHERE...VFR CONDITIONS WILL PREVAIL...EXCEPT IN
THE VICINITY OF AFTERNOON BUILDUPS WHERE ISOL MVFR COND AND BRIEF
MTN OBSC WILL OCCUR IN SHOWERS.

AIRMET ZULU IS IN EFFECT FOR LIGHT ICING NEAR THE CLOUD TOPS AROUND
THE BIG ISLAND.

&&

.MARINE...
WINDS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS
THROUGH THE WORK WEEK. THE SURFACE RIDGE REBUILDS NORTH OF THE
STATE BY THE WEEKEND...AND WINDS ARE EXPECTED TO INCREASE AGAIN
DURING THE WEEKEND. SMALL CRAFT CONDITIONS ARE POSSIBLE ACROSS THE
TYPICALLY WINDIER AREAS NEAR MAUI AND THE BIG ISLAND IF THE MODEL
SOLUTIONS HOLD TRUE.

SMALL SWELLS ORIGINATING FROM THE SOUTHERN HEMISPHERE WILL CONTINUE
TO MAINTAIN BACKGROUND SURF ALONG SOUTH FACING SHORES THIS WEEK. A
SMALL LONG PERIOD SOUTHWEST SWELL ARRIVING LATE FRIDAY MAY PRODUCE A
SMALL BUMP IN SURF HEIGHTS ALONG SOUTH FACING SHORES THIS WEEKEND. A
LARGER SOUTH SWELL MAY ARRIVE LATE MONDAY INTO TUESDAY.
ELSEWHERE...A MODERATE EASTERLY TRADE SWELL WILL SLOWLY SUBSIDE
THROUGH THE WEEK AS THE TRADE WINDS WEAKEN...THEN PICK UP AGAIN TO
MODERATE LEVELS OVER THE WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

DISCUSSION...R BALLARD
AVIATION...EVANS/MORRISON
MARINE...BRAVENDER