Heavy Rain in Hawaii, April 19 to 21, 2009

Name: Heavy Rain in Hawaii, April 19 to 21, 2009
Start: 2009-04-19T12:34
End: 2009-04-21T07:34
Location: Hawaii

April 19 to 21, 2009 · NWS HFO · 6 events in 3 counties and zones

A cold front moving through the state generated heavy showers from Kauai to Maui. The system caused ponding of roadways, and small stream and drainage ditch flooding.

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

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 6

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 cold front moving through the state generated heavy showers from Kauai to Maui. The system caused ponding of roadways, and small stream and drainage ditch flooding. However, no significant property damage or injuries were reported.

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 Apr 19, 10:30 AM HST, 2 hours 4 minutes earlier.

Area forecast discussion, Apr 19, 10:30 AM HST, 2 hours 4 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1030 AM HST SUN APR 19 2009

.SYNOPSIS...
A COLD FRONT IS APPROACHING THE ISLANDS FROM THE NORTHWEST. A BAND
OF CLOUDS AND SHOWERS FORMING AHEAD OF THE FRONT WILL BRING BRIEFLY
HEAVY SHOWERS TO KAUAI TODAY...BEFORE THE FRONT ARRIVES TONIGHT. THE
FRONT WILL MOVE TO OAHU ON MONDAY...MAUI COUNTY MONDAY NIGHT...AND
THEN STALL OVER THE ISLANDS FROM TUESDAY THROUGH THURSDAY. SHOWERS
ALONG THE FRONT MAY BECOME HEAVY ON MONDAY NIGHT AND TUESDAY...WITH
THESE HEAVY SHOWERS FOCUSED OVER WINDWARD SLOPES. WINDS AHEAD OF THE
FRONT WILL BE SOUTHWEST AND WEST...AND WILL SHIFT TO THE NORTH AND
NORTHEAST AFTER THE FRONT PASSES.

&&

.DISCUSSION...
A COLD FRONT APPROACHING FROM THE NORTHWEST IS ABOUT 200 MILES WEST
AND NORTHWEST OF KAUAI...AND A BAND OF PRE-FRONTAL CLOUDS AND
SHOWERS IS OVER LEEWARD KAUAI COASTAL WATERS...MOVING TOWARD KAUAI.
HAVE UPDATED FORECASTS AND ISSUED A MARINE WEATHER STATEMENT TO
ACCOUNT FOR THESE DEVELOPMENTS. GLOBAL MODELS CONTINUE TO DIFFER ON
THE SPEED OF MOVEMENT OF THESE BOUNDARIES DOWN THE ISLAND
CHAIN...AND WHERE THE FRONT EVENTUALLY STALLS.

FOR NOW...FORECAST PHILOSOPHY MOVES THE FRONT OVER KAUAI AFTER
SUNSET TONIGHT...TO OAHU OVERNIGHT AND MONDAY...AND TO MAUI AND
HAWAII COUNTIES MONDAY NIGHT AND TUESDAY. WINDS AHEAD OF THE FRONT
WILL BE LIGHT TO MODERATE FROM THE SW AND W...AND WILL SHIFT TO THE
N AND NE AFTER THE FRONT PASSES. AS THE PARENT LOW /BOTH ALOFT AND
SURFACE/ WILL BE CUTTING OFF TO THE NORTHEAST OF THE ISLANDS FOR
MOST OF THE WEEK...BRISK NE FLOW INITIALLY BEHIND THE FRONT WILL
GRADUALLY WEAKEN...AND THE FRONT WILL TAKE IT/S TIME IN LEAVING THE
LATITUDE OF THE ISLANDS ONCE IT ARRIVES.

THE MID-LEVEL TROUGH THAT IS CURRENTLY SUPPORTING THE FRONT AND
PARENT LOW WILL BECOME A WELL-DEVELOPED CUT-OFF LOW...CENTERED ABOUT
800 MILES NORTHEAST OF THE ISLANDS...BY TONIGHT. BOTH GFS AND ECMWF
ARE NOW INDICATING THAT A SHORT WAVE WILL ROTATE AROUND THE BASE OF
THE LOW ON MONDAY NIGHT AND TUESDAY...IGNITING CONVECTION ALONG THE
FRONTAL BOUNDARY...AND POTENTIALLY CAUSING THE DEVELOPMENT OF HEAVY
SHOWERS. NE WINDS BEHIND THE FRONT WILL FOCUS THIS RAINFALL OVER
WINDWARD SLOPES...AND WILL EVALUATE MODEL OUTPUT TODAY BEFORE MAKING
SIGNIFICANT CHANGES TO THE FORECAST.

IN THE MID-LEVELS...A TIGHT GRADIENT WILL MAINTAIN ADVISORY LEVEL
WINDS OVER THE BIG ISLAND SUMMITS AND UPPER ELEVATIONS FOR AT LEAST
THE NEXT COUPLE OF DAYS.

AFTER THE CUT-OFF LOW WEAKENS AND MOVES OFF TO THE NORTHEAST
THURSDAY AND FRIDAY...A NEW LOW ALOFT MAY DEVELOP WEST AND OVER THE
ISLANDS NEXT WEEKEND. IF THIS IS CORRECT...CONDITIONS MAY BECOME WET
AND UNSETTLED AGAIN.

&&

.MARINE...
THE SURFACE LOW WILL DELIVER A SHORT-PERIOD NORTH-NORTHEAST SWELL
WHICH WILL BUILD ON TUESDAY...PEAK ON WEDNESDAY AND THURSDAY...AND
LOWER ON FRIDAY AND SATURDAY. THE SWELL WILL LIKELY BE LARGE ENOUGH
TO EXCEED THE 8 FOOT ADVISORY THRESHOLD ALONG EAST FACING SHORES.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY FOR MAUNA KEA AND MAUNA LOA SUMMITS UNTIL 10 AM HST
MONDAY.

&&

BIRCHARD

The radar

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

Open the radar archive at this moment

Event by event

6 heavy rain. Local standard time, as filed.

Heavy Rain, Kauai

When: April 19, 12:34 PM HST to 5:12 PM HST
Where: Kauai County, 1.62 mi ESE of Na Pali Coast Sp to 0.57 mi NW of Port Allen
Reported by: Official NWS Observations
Coordinates: 22.170, -159.627

Heavy Rain, Kauai

When: April 20, 12:12 PM HST to 2:20 PM HST
Where: Kauai County, 2.67 mi WNW of Hanalei to 1.15 mi SW of Lawai
Reported by: Official NWS Observations
Coordinates: 22.212, -159.540

Heavy Rain, Honolulu

When: April 20, 12:35 PM HST to 3:20 PM HST
Where: Honolulu County, 2.49 mi NW of Hauula to 0.91 mi WNW of Nanakuli
Reported by: Official NWS Observations
Coordinates: 21.646, -157.927

Heavy Rain, Maui

When: April 20, 8:40 PM HST to April 21, 7:34 AM HST
Where: Maui County, 1.19 mi ESE of Honokohau to 2.81 mi WNW of Waianapanapa Sp
Reported by: Official NWS Observations
Coordinates: 21.010, -156.605

Heavy Rain, Honolulu

When: April 20, 9:55 PM HST to April 21, 12:59 AM HST
Where: Honolulu County, 0.54 mi NNE of Waikane to 0.84 mi S of Hawaii Kai
Reported by: Official NWS Observations
Coordinates: 21.507, -157.878

Heavy Rain, Maui

When: April 20, 10:50 PM HST to April 21, 4:41 AM HST
Where: Maui County, 0.52 mi S of Kalaupapa to 1.32 mi SSW of Cape Halawa
Reported by: Official NWS Observations
Coordinates: 21.192, -156.981

What these are

Heavy Rain: Rainfall totals unusual for the place and season that did not produce a flood.

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, April 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: 158301, 158302, 158303, 158304, 158305, 158306.