Flash Flood and Heavy Rain in Hawaii, July 22 to 23, 2009

Name: Flash Flood and Heavy Rain in Hawaii, July 22 to 23, 2009
Start: 2009-07-22T14:49
End: 2009-07-23T19:10
Location: Hawaii

July 22 to 23, 2009 · NWS HFO · 2 events in 2 counties and zones

A surface trough, moving from east to west, induced heavy rain and showers over the islands. There were no reports of serious property damage or injuries.

Where it happened

Every event with a place to put it. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

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The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 2

Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.

What happened

The episode as NWS HFO wrote it up.

A surface trough, moving from east to west, induced heavy rain and showers over the islands. There were no reports of serious property damage or injuries.

What forecasters said that day

The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Honolulu, HI wrote its last area forecast discussion before the first event at Jul 22, 10:00 AM HST, 4 hours 49 minutes earlier.

Area forecast discussion, Jul 22, 10:00 AM HST, 4 hours 49 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST WED JUL 22 2009

.SYNOPSIS...
THE TRADE WINDS WILL GRADUALLY DIMINISH OVER THE NEXT SEVERAL
DAYS...ALLOWING FOR PERIODS OF LIGHT AND VARIABLE WINDS. A TROUGH
JUST EAST OF THE STATE COULD BRING HEAVY RAIN TO THE BIG ISLAND AND
PERHAPS MAUI. A MORE TYPICAL TRADE WIND WEATHER SCENARIO WILL RETURN
BY EARLY NEXT WEEK...ONCE THE TROUGH MOVES WEST OF THE ISLANDS.

&&

.DISCUSSION...
A SURFACE TROUGH EMBEDDED IN THE TRADE FLOW EAST OF THE BIG ISLAND
IS MOVING SLOWLY TO THE WEST. SATELLITE AND NEXRAD DETECT ISOLATED
THUNDERSTORMS AND NUMEROUS SHOWERS STRUNG OUT NORTHEAST TO SOUTHWEST
EAST OF THE STATE. POES AMSU/SSMI SATELLITE TOTAL PRECIPITABLE WATER
FIELDS CONTINUE TO SHOW HIGH VALUES OF 2 TO 2.5 INCHES. THE LOCALLY
HEAVY RAIN IN THE FORECAST FOR THE WINDWARD BIG ISLAND AND MAUI
ALLOWS FOR THE PASSAGE OF THE TROUGH.

THE OVERALL FORECAST REASONING REMAINS UNCHANGED. DECREASING TRADE
WINDS ARE EXPECTED INTO THE WEEKEND DUE TO THE WESTWARD MOVING
SURFACE TROUGH MENTIONED ABOVE AND AN EASTWARD MOVING TROUGH FAR
NORTH OF THE STATE. THE TWO TOGETHER WILL FLATTEN THE TRADEWIND
DRIVING SUBTROPICAL RIDGE TO OUR NORTH. THE RESULTANT FORECAST IS
AN ATTEMPT AT MIXING A DIURNAL CONVECTIVE PATTERN AND A LIGHT TRADE
WIND PATTERN. HAVE LITTLE CONFIDENCE IN THE SMALL SCALE DETAILS...
BUT REASONABLE CONFIDENCE IN THE SHORT TERM TRENDS. THE RIDGE IS
FORECAST TO STRENGTHEN OVER THE WEEKEND ALLOWING THE RETURN OF
MODERATE TRADE WINDS ON SUNDAY AT THE EARLIEST.

&&

.MARINE...
THE SMALL CRAFT ADVISORY WILL CONTINUE FOR THE WINDIER AREAS THROUGH
TODAY. THE WINDS SHOULD HOWEVER DECREASE FROM EAST TO WEST AS THE
TROUGH APPROACHES FROM THE EAST.

LATEST THINKING ON A NEW SOUTH SWELL IS THAT IT WILL PLATEAU NEAR 8
FEET THIS AFTERNOON...MAYBE LATE. SURF HEIGHTS SHOULD HOLD THROUGH
THURSDAY AFTERNOON/EVENING.

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

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST TODAY FOR MAALAEA BAY-PAILOLO
CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG ISLAND
SOUTHEAST WATERS.

HIGH SURF ADVISORY FROM UNTIL 6 PM HST THURSDAY FOR SOUTH FACING
SHORES.

&&

CRAIG

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

1 heavy rain, 1 flash flood. Local standard time, as filed.

Heavy Rain, Maui

When: July 22, 2:49 PM HST to 5:42 PM HST
Where: Maui County, 0.8 mi WSW of Kahakuloa to 1.84 mi NNW of Hamoa
Reported by: Official NWS Observations
Coordinates: 20.995, -156.561

Flash Flood, Kauai

When: July 23, 10:41 AM HST to 7:10 PM HST
Where: Kauai County, 0.66 mi SSE of Princeville to 0.69 mi SSE of Princeville
Cause: Heavy Rain
Reported by: Law Enforcement
Coordinates: 22.211, -159.476

Heavy rain caused flooding along the Hanalei River, forcing the closure of the Hanalei Bridge for a time in the northern part of Kauai.

What these are

Heavy Rain: Rainfall totals unusual for the place and season that did not produce a flood.
Flash Flood: Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Hawaii in 2009 Every state in 2009 This day in weather history Warnings in Hawaii, July 2009

Sources

NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 180160, 180162.