Heavy Rain in Hawaii, April 20, 2004

Name: Heavy Rain in Hawaii, April 20, 2004
Start: 2004-04-20T21:50
End: 2004-04-20T23:50
Location: Hawaii

April 20, 2004 · NWS HFO · 1 event in 1 county or zone

Heavy showers in and around Ulupalakua on Maui produced drainage ditch and small stream flooding, and ponding of roadways. There were no reports of serious injuries or property damage.

Where it happened

Every event with a place to put it; 1 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

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The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 1

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.

Heavy showers in and around Ulupalakua on Maui produced drainage ditch and small stream flooding, and ponding of roadways. There were no reports of serious injuries or property damage.

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 20, 8:30 PM HST, 1 hour 20 minutes earlier.

Area forecast discussion, Apr 20, 8:30 PM HST, 1 hour 20 minutes before

HAWAIIAN ISLANDS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST TUE APR 20 2004

.SYNOPSIS...
WINDS WILL BE LIGHT AND VARIABLE OVERNIGHT AS A TROUGH WEAKENS A
RIDGE TO OUR NORTH. THE TRADES WILL RETURN LATE WEDNESDAY WHEN THE
TROUGH MOVES TO THE NORTH AND THE RIDGE RECOVERS. TRADE WIND WEATHER
WILL LAST FROM THURSDAY ONWARD...WITH SHOWERS FAVORING WINDWARD AND
MAUKA AREAS.

&&

.DISCUSSION...
A SURFACE TROUGH EXTENDING SOUTH FROM A LOW IN THE ALEUTIAN ISLANDS
HAS WEAKENED THE SUBTROPICAL RIDGE. THIS WEAKENED PORTION OF THE
RIDGE IS EXPECTED TO PASS NORTH OF THE ISLANDS TONIGHT AND EARLY
WEDNESDAY...KEEPING OUR WINDS LIGHT AND VARIABLE. BY WEDNESDAY
EVENING THE TROUGH WILL LIFT NORTHWARD...ALLOWING THE RIDGE TO
REBOUND AND INDUCE 10 TO 20 MPH TRADES. A SECOND TROUGH IN THE
WESTERLIES WILL BE NORTH OF HAWAII SATURDAY...BUT SHOULD NOT DIG FAR
ENOUGH SOUTH TO WEAKEN OUR WINDS. A 1030 MB HIGH EXPECTED TO MOVE
EASTWARD WITHIN THE RIDGE BEHIND THIS SECOND TROUGH WILL BOOST THE
TRADES OVER THE WESTERN ISLANDS IN THE MIDDLE OF NEXT WEEK.

AN UPPER TROUGH OVERHEAD HAS CONTRIBUTED SOME INSTABILITY WHICH IN
TURN HAS ENHANCED THE SHOWERS IN THE AREA. THE TROUGH WILL MOVE
EASTWARD AND WE WILL SEE DRIER TRADES FROM THURSDAY THROUGH THE
WEEKEND.

&&

.SURF...
WE ARE STILL EXPECTING A LARGE SOUTH SWELL TO ARRIVE SATURDAY AND
LAST INTO SUNDAY WITH WAVE HEIGHTS PERHAPS REACHING WARNING LEVELS.
WE SHOULD GET A BETTER IDEA ON JUST HOW HIGH THE SURF WILL GET
THURSDAY WHEN THE SWELL PASSES UNDER BUOY 28 LOCATED ON THE EQUATOR
SOUTH OF THE BIG ISLAND.

&&

.WATCHES/WARNINGS/ADVISORIES...
NONE.

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. Local standard time, as filed.

Heavy Rain, Maui

When: April 20, 9:50 PM HST to 11:50 PM HST
Where: Maui County, Ulupalakua
Reported by: OFFICIAL NWS OBS.
Coordinates: 20.868, -156.617 (the zone’s center; the record gives no point)

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 2004 Every state in 2004 This day in weather history Warnings in Hawaii, April 2004

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: 5431399.