Monthly Climate and Impacts Report for Hawaii - September 2012

Chris O'Connor and Dr. Pao-Shin Chu
Hawaii State Climate Office
Department of
University of Hawaii
Honolulu, HI 96822

Precipitation and Temperature

September 2012 was drier than normal, as we saw the currently ongoing dry trend continue. This dry trend was present throughout the entire summer and is now bleeding into the early autumn months. On Oahu and Kauai we saw minimal rainfall around the early to middle part of the month, and dry conditions throughout the remainder of the month. Maui was abnormally dry the entire month, other than September 20th; when the island experienced fairly significant precipitation. Hilo saw a consistent trend of rainfall all month, however experienced overall lower than normal precipitation. All four airports reported rainfall significantly below their normal totals. Drought conditions across the state remained approximately the same from last month, with Oahu and Kauai ranging from "Abnormally Dry" (D0) to "Severe Drought" (D2), while the eastern islands have areas ranging from "Abnormally Dry" (D0) to "Extreme Drought" (D3) on a scale of D0-D4. Interestingly, Niihau is completely drought free, as well as northeastern shores of Oahu, Maui and Hawai'i.

Across the state, mean temperatures as well as mean highs and mean lows were below their respective historical averages.   Generally this is a sign of increased cloudiness blocking both incoming solar radiation and outgoing longwave radiation, effectively reducing the diurnal temperature range. This is confirmed by observations, all four airports had more than 19 days as "partly cloudy" or cloudier.

The NOAA Climate Prediction Center seasonal outlook for Hawaii predicted below normal precipitation and below normal temperatures for the entire state in October 2012.


After experiencing La Nina conditions the past two winters, we are now identifying a shift in the behavior of the ENSO cycle. Positive Sea-Surface-Temperatures have been recorded since April 2012, triggering a shift from La Nina conditions to ENSO-neutral conditions. The general consensus is that we are in fact seeing a possible weak El Nino formation for next winter, however since the beginning of September, positive SST anomalies have weakened. NOAA is still forecasting a 70% probability for El Nino conditions to develop and a 30% probability for ENSO-neutral conditions to develop this winter.


The Hawaiian weather was very dry throughout the month and the effects of drought are continuing to be felt state-wide.  As a result, voluntary restrictions on water use remains in place as a precaution for the dry season.  On Kauai, the area of drought impacts have been spreading westward.  This is reflected in the most recent U.S. Drought Monitor maps, resulting in a downgrade from D2 (severe drought) to D3 (extreme drought) on the leeward slopes of the island. Oahu is experiencing similar impacts to recent months: poor condition of pastures and visible dryness of the landscape. Molokai is experiencing such dryness that the State of Hawaii Department of Agriculture has continued a mandatory 30% reduction in irrigation water consumption. The island itself has been very dry and suffering from low water levels in reservoirs, especially the Kualapuu Reservoir. Lanai vegetation is struggling through the drought conditions as reports from the island indicate that even drought-resistant plants and trees such as Kiawe were struggling under the dry circumstances. The same story of poor general vegetation and struggling ranchers due to low precipitation levels persists on Maui and Hawai'i. The general consensus: our islands of Hawai'i desperately need significant precipitation.