Heavy Rain, Honolulu
- When
- July 21, 2:39 AM HST to 6:24 AM HST
- Where
- Honolulu County, 1.09 mi W of Kahuku to 1.68 mi W of Kailua
- Reported by
- Official NWS Observations
- Coordinates
- 21.681, -157.967
Flash Flood and Heavy Rain in Hawaii, July 21 to 22, 2015
Upper level instability acted on low level moisture to produce heavy showers and isolated thunderstorms over the western part of the Aloha State. The rain was heavy enough to cause flash flooding on Kauai near Hanalei as the Hanalei River overflowed onto Kuhio Highway near the Hanalei Bridge.
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
The toll
- Deaths
- 0
- Injuries
- 0
- Property damage
- None recorded
- Crop damage
- None recorded
- Events
- 3
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.
Upper level instability acted on low level moisture to produce heavy showers and isolated thunderstorms over the western part of the Aloha State. The rain was heavy enough to cause flash flooding on Kauai near Hanalei as the Hanalei River overflowed onto Kuhio Highway near the Hanalei Bridge. However, 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 Jul 20, 11:00 PM HST, 3 hours 39 minutes earlier.
Area forecast discussion, Jul 20, 11:00 PM HST, 3 hours 39 minutes before
AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE HONOLULU HI 1100 PM HST MON JUL 20 2015 .UPDATE...UPDATED AVIATION SECTION. && .SYNOPSIS... LIGHT WINDS ARE EXPECTED ACROSS THE STATE THROUGH MID WEEK...ALLOWING LOCALIZED LAND AND SEA BREEZES. THE LIGHTER WINDS WILL BRING A GREATER CHANCE OF AFTERNOON CLOUDS AND SHOWERS OVER LEEWARD AND INTERIOR PORTIONS OF ALL ISLANDS. A TROUGH ALOFT DEVELOPING JUST WEST OF THE ISLANDS MAY HELP TO ENHANCE SHOWERS THROUGH THE MIDDLE OF THE WEEK. TRADE WINDS WILL SLOWLY STRENGTHEN DURING THE SECOND HALF OF THE WEEK...WITH SHOWERS ONCE AGAIN FOCUSED OVER WINDWARD AREAS. && .DISCUSSION... TRADE WINDS CONTINUE TO BE ON THE DECLINE THIS EVENING ACROSS THE ISLANDS AS THE PRESSURE GRADIENT RELAXES ACROSS THE STATE. THERE ARE SOME LOW CLOUDS EMBEDDED IN THE WIND FLOW PASSING OVER THE ISLANDS AT TIMES...AFFECTING MAINLY WINDWARD AREAS. ALSO LOW CLOUDS FROM THE AFTERNOON CONVECTION OVER MAUI AND THE BIG ISLAND WILL LINGER THROUGH EARLY THIS EVENING...AND SHOULD CLEAR A BIT AS THE NIGHT PROGRESSES. THE AIRMASS IN THE ISLAND VICINITY IS SLIGHTLY UNSTABLE...AS A BROAD UPPER LEVEL TROUGH JUST WEST OF THE ISLANDS DEEPENS A LITTLE IN THE NEXT COUPLE OF DAYS. EXPECT SOME OF THE SHOWERS TO BE ENHANCED...BRINGING SOME LOCALIZED MODERATE PRECIPITATION. THE LIGHT WIND WEATHER SCENARIO WILL CONTINUE ACROSS THE STATE THROUGH THE NEXT COUPLE OF DAYS...WITH MORE WIDESPREAD LAND AND SEA BREEZES TO DEVELOP OVER THE ISLANDS DURING NIGHT AND DAY. AFTERNOON CLOUDS AND SHOWERS WILL DEVELOP OVER THE ISLANDS UNDER SEA BREEZES...AND SINCE THE AIRMASS IN THE ISLAND VICINITY WILL REMAIN SOMEWHAT UNSTABLE...EXPECT POSSIBLE ENHANCEMENT OF THE SHOWERS. IN FACT...THERE WILL ALSO BE A SLIGHT CHANCE OF AFTERNOON THUNDERSTORMS OVER THE BIG ISLAND...MAINLY OVER THE WESTERN PORTION. DURING THE SECOND HALF OF THE WEEK...THE PRESSURE GRADIENT ACROSS THE STATE WILL TIGHTEN. THE ISLANDS WILL SEE A RETURN OF STRONGER TRADE WINDS. AS THE WINDS STRENGTHEN...THE SHOWERS WILL ONCE AGAIN BECOME FOCUSED OVER WINDWARD AND MAUKA AREAS. THE LONG RANGE GUIDANCE CONTINUE TO HINT MOISTURE ASSOCIATED WITH THE REMNANTS OF FORMER EAST PACIFIC TROPICAL CYCLONE ENRIQUE MAY REACH THE ISLANDS DURING THE WEEKEND. IF SO...AN INCREASE IN SHOWERS AS WELL AS HUMIDITY MAY BE IN STORE FOR THE STATE OVER THE WEEKEND. && .AVIATION... VFR CONDITIONS WILL PREVAIL AT THE TERMINALS OVERNIGHT. HOWEVER...LINGERING CLOUD COVER ACROSS MOUNTAINOUS TERRAIN MAY PRODUCE LOCAL AND BRIEF MVFR OR LOWER CONDITIONS AS IT SLOUGHS OFF ACROSS ADJACENT WATERS. AIRMET SIERRA FOR MOUNTAIN OBSCURATION IS IN EFFECT THROUGH TONIGHT FOR MAUI AND THE BIG ISLAND SINCE AT LEAST TEMPORARY MOUNTAIN OBSCURATION IS APPARENT BELOW 3000 FEET. && .MARINE... WINDS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY /SCA/ CRITERIA THROUGH AT LEAST MID WEEK. AS THE TRADES STRENGTHEN DURING THE SECOND HALF OF THE WEEK...SCA CONDITIONS MAY OCCUR OVER THE TYPICAL WINDIER LOCATIONS NEAR MAUI AND THE BIG ISLAND. SURF ALONG EAST FACING SHORES WILL REMAIN ELEVATED THROUGH THURSDAY...PEAKING WEDNESDAY...AS A NEW NE SWELL ARRIVES WHILE THE EXISTING EAST SWELLS CONTINUE. SURF FOR EAST FACING SHORES IS EXPECTED TO INCREASE TO JUST BELOW ADVISORY LEVELS THROUGH WEDNESDAY. A PERSISTENT STORM SYSTEM IN THE SOUTH PACIFIC EAST OF NEW ZEALAND DEVELOPED A COUPLE OF DAYS AGO HAS BEEN GENERATING LARGE SWELL TOWARD HAWAII. THIS SWELL IS ANTICIPATED TO ARRIVE IN HAWAII FRIDAY AND WILL LIKELY BE LARGE ENOUGH TO BRING ADVISORY LEVEL SURF HEIGHTS ALONG SOUTH FACING SHORES THIS WEEKEND. PLEASE REFER TO THE SURF DISCUSSION /SRDHFO/ DISCUSSION FOR MORE DETAILS. && .HFO WATCHES/WARNINGS/ADVISORIES... NONE. && DISCUSSION/MARINE...HUI AVIATION...POWELL
The radar
The Molokai radar (PHMO), 102 km away, was scanning. The volume nearest the first event began at 12:38 UTC.
Event by event
2 heavy rain, 1 flash flood. Local standard time, as filed.
Heavy Rain, Kauai
- When
- July 21, 11:15 AM HST to 5:07 PM HST
- Where
- Kauai County, 0.81 mi ENE of Pokii to 4.4 mi NW of Anahola
- Reported by
- Official NWS Observations
- Coordinates
- 21.984, -159.708
Flash Flood, Kauai
- When
- July 22, 12:35 PM HST to 2:24 PM HST
- Where
- Kauai County, 0.66 mi S of Princeville to 0.77 mi SSE of Princeville
- Cause
- Heavy Rain
- Reported by
- Emergency Manager
- Coordinates
- 22.210, -159.480
Kauai Civil Defense reported water crossing Kuhio Highway near the Hanalei Bridge.
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
- Flash Flooding and Flooding in Kansas, July 21, 2015
- Damaging Winds and Lightning Strike in Florida, July 21 to 25, 2015
- Damaging Winds in Georgia, July 21 to 23, 2015
- Damaging Winds in New York, July 21, 2015
- Hail and Damaging Winds in North Carolina, July 21, 2015
- Flood and Damaging Winds in Florida, July 21, 2015
- Tornado and Damaging Wind in Colorado, July 21, 2015
- Damaging Winds in North Carolina, July 21, 2015
- Lightning Strike in New Jersey, July 21, 2015
- Damaging Wind in Connecticut, July 21, 2015
- Damaging Winds and Lightning Strike in North Carolina, July 21, 2015
- Damaging Winds in South Carolina, July 21, 2015
More
Every storm in Hawaii in 2015Every state in 2015This day in weather historyWarnings in Hawaii, July 2015
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: 585929, 585930, 585931.