Heavy Rain in Hawaii, August 20 to 22, 2012

Name: Heavy Rain in Hawaii, August 20 to 22, 2012
Start: 2012-08-20T06:29
End: 2012-08-22T17:16
Location: Hawaii

August 20 to 22, 2012 · NWS HFO · 2 events in 2 counties and zones

A low- to mid-level trough helped enhance showers over windward Big Island and leeward East Maui. There was minor drainage ditch and stream flooding, and ponding on roadways.

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 low- to mid-level trough helped enhance showers over windward Big Island and leeward East Maui. There was minor drainage ditch and stream flooding, and ponding on roadways. 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 Aug 20, 6:26 AM HST, 3 minutes earlier.

Area forecast discussion, Aug 20, 6:26 AM HST, 3 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
626 AM HST MON AUG 20 2012

.UPDATE...
HAVE ADDED IN SOME SHOWERS FOR THE BIG ISLAND SUMMITS THIS MORNING
AS WEB CAMS AND SURFACE OBSERVATIONS INDICATE SOME LIGHT SHOWER
ACTIVITY IS OCCURRING AT THIS TIME.

&&

.SYNOPSIS...
HIGH PRESSURE REMAINS CENTERED TO THE NORTH OF THE AREA AND KEEPING
MODERATE TRADE WIND FLOW THROUGH THE END OF THE WEEK. SHOWERS WILL
FAVOR WINDWARD AND MOUNTAIN AREAS...MAINLY NIGHTS AND MORNINGS. AN
AREA OF ENHANCED SHOWERS WILL CONTINUE TO MOVE ACROSS THE WINDWARD
AREAS OF THE BIG ISLAND AND MAUI TODAY. IN ADDITION...EXPECT
AFTERNOON AND EVENING SHOWERS FOR THE KONA SIDE OVER THE BIG ISLAND
EACH DAY. DRIER CONDITIONS WILL PREVAIL OVER LEEWARD AREAS OF THE
SMALLER ISLANDS.

&&

.PREV DISCUSSION.../ISSUED 345 AM HST MON AUG 20 2012/

A BROAD 1024 MB HIGH REMAINS CENTERED TO THE NORTH OF THE MAIN
HAWAIIAN ISLANDS AND PROVIDING FOR A MODERATE TRADE WIND REGIME
ACROSS THE AREA. AT 325 AM HST 88D/IR SAT DATA WERE SHOWING AN AREA
OF ENHANCED RAIN STILL AFFECTING PORTIONS OF THE EAST SIDE OF THE
BIG ISLAND...WITH ADDITIONAL SHOWERS UPSTREAM TO MOVE ACROSS THE BIG
ISLAND AND WINDWARD MAUI THROUGH LATER THIS MORNING.

WINDS OVER THE HALEAKALA SUMMIT HAVE DECREASED TO BELOW ADVISORY
LEVELS. THEREFORE...THE WIND ADVISORY HAS BEEN CANCELLED.

THE STRONG SURFACE HIGH PRESSURE NORTH OF THE ALOHA STATE WILL
KEEP THE PREVAILING TRADE WIND FLOW IN PLACE THROUGH THE
FORECAST PERIOD WITH BEST CHANCES FOR RAIN REMAINING OVER WINDWARD
AND MAUKA AREAS. HOWEVER...AFTERNOON CLOUD COVER IS EXPECTED TO
INCREASE OVER THE KONA SIDE OF THE BIG ISLAND AS ONSHORE FLOW
RETURNS EACH DAY. ALSO...SOME AREAS ACROSS THE WESTERN OAHU COAST
COULD ALSO SEE MORE AFTERNOON CLOUD COVER.

EARLIER MODEL GUIDANCE WAS SUGGESTING POTENTIAL FOR ENHANCED
CONVECTIVE ACTIVITY BY THE END OF THE WEEK WITH INCREASING LI AND
MOISTURE VALUES. BUT DIFFERENCES BETWEEN MODELS REGARDING COVERAGE
AND TIMING ARE KEEPING A LOW LEVEL OF CONFIDENCE IN THIS SOLUTION
FOR THE LONG TERM FORECAST. THEREFORE...WILL REFRAIN FROM
INCORPORATING SIGNIFICANT CHANGES TO INHERITED LONG RANGE POPS AT
THIS TIME AND WAIT FOR UPCOMING MODEL GUIDANCE.

&&

.AVIATION...
VFR CONDITIONS WILL DOMINATE MOST TAF SITES...EXCEPT FOR AN AREA OF
SHOWERY LOW CLOUDS AFFECTING THE BIG ISLAND AND THE ISLANDS OF MAUI
COUNTY CREATING AREAS OF MVFR/IFR FROM TIME TO TIME. AN AIRMET IS
IN EFFECT FOR TEMPORARY MT OBSCURATION ALONG NORTHEAST-FACING SLOPES
OF MAUI AND THE BIG ISLAND...A CONDITION EXPECTED TO CONTINUE
THROUGH TODAY.

&&

.MARINE...
A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR THE ALENUIHAHA
CHANNEL...PAILOLO CHANNEL AND MAALAEA BAY UNTIL MONDAY AFTERNOON
WITH WIND SPEEDS UP TO 25 KNOTS. ELSEWHERE...THE TRADE WINDS SHOULD
REMAIN MARGINAL.

THERE ARE NO SIGNIFICANT SWELLS OR SURF EXPECTED ACROSS THE COASTAL
WATERS THROUGH THE REST OF THE FORECAST PERIOD.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST THIS EVENING FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL.

&&

UPDATE...BURKE
SYNOPSIS/DISCUSSION/MARINE...REYNES/DONALDSON
AVIATION...POWELL

The radar

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

Open the radar archive at this moment

Event by event

2 heavy rain. Local standard time, as filed.

Heavy Rain, Hawaii

When: August 20, 6:29 AM HST to 9:23 AM HST
Where: Hawaii County, 2.91 mi SSE of Pahoa to 6.82 mi NNW of Kamuela
Reported by: Official NWS Observations
Coordinates: 19.459, -154.959

Heavy Rain, Maui

When: August 22, 3:05 PM HST to 5:16 PM HST
Where: Maui County, 1.93 mi ESE of Makena to 2.38 mi S of Pulehu
Reported by: Official NWS Observations
Coordinates: 20.656, -156.404

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 2012 Every state in 2012 This day in weather history Warnings in Hawaii, August 2012

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: 397972, 397973.