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Wet Season Rainfall Outlook for Hawaii

October 18, 2010, 10:09 AM HST
* Updated October 18, 10:14 AM
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Summary of dry season
• Statewide: Drought worsened
o “Exceptional drought” (D4 category in U.S. Drought Monitor) spread to Kau
o “Moderate drought” (D1 category) went from 50% in May to 74% September
• Leeward Big Island “severe” (D2 category) to “exceptional” drought
o Worst conditions in South Kohala and south Kau
o Some improvement in Kona coffee belt from summer rainfall
• Drought broadly affecting agriculture
o Livestock, orchards, crops, ornamentals affected
• Windward rainfall frequency near normal but daily totals below normal
• Hilo and Kapapala Ranch remain on pace for driest year on record.
o Hilo: 37.05 inches through September, normal is over 90 inches.
 Record driest year: 1983, 68.09 inches
o Kapapala Ranch: 5.41 inches through September, normal is 42 inches.
 Record driest year: 1998, 13.42 inches

Outlook for wet season
• Climate Prediction Center (CPC): La Nina is the primary influence
o Drier than normal through November
o Wetter than normal January through April/May
o More uncertainty compared to last year’s forecast with El Nino
• Previous wet seasons with moderate/strong La Nina
o 1999, 2000, 2008 are most recent examples
o Higher than normal frequency of trades
o Occasional upper level lows produced heavy rainfall
o Wet conditions primarily affected windward areas
o Leeward areas remained dry during 1999 & 2000 events
• Drought recovery more likely on smaller islands (Kauai to Molokai) and over windward slopes of Big Island and Maui
• Possibility of drought to continue through the wet season, especially over leeward areas if conditions similar to 1999 and 2000.

Wet season preparedness
• Clean gutters and drainage ditches
• If you live in a flood-prone area, identify your evacuation routes ahead of time
• Plan for more rainy weather impacts
o Increased road travel times or possible detours due to flooding
o Outdoor activities may be postponed, canceled, or adjusted
• Increased potential for lightning strikes
o Be prepared for possible power outages
o Move indoors during a thunderstorm
• Do you have a NOAA Weather Radio?

On the Web:
NOAA National Weather Service Honolulu HI:
Hawaii Dry Season (May – September) Maps
Molokai and Lanai:
Big Island:

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