MONTHLY PRECIPITATION SUMMARY State of Hawaii portion of Honolulu HSA MONTH: January 1998 PREPARED February 2, 1998 State: No significant Flash flooding was reported. Significant drought conditions established on the Island of Hawaii and developing elsewhere across the state. Below average precipitation occurred state wide with all first order and automated rain gages receiving less than average rainfall in January. Hawaii has four first order National Weather Service Offices and 69 automated rain gage stations. 63 of these 73 reported less than 50 percent of average rainfall for the month of January with 36 of the 73 receiving less than 25 percent of average for the month. This continued the three to four month trend state wide of drier than usual conditions. January 1998 weather patterns were dominated by multiple upper level high pressure ridges over and to the west of the islands. This strong upper level ridge pattern and its effects on the limited precipitation pattern is clearly indicating the effects of the El Nino phenomena on the islands. In Hawaii, below average precipitation is frequently observed in the last half of the wet season of the onset year and much of the following years wet season is also below average according to studies(Chu, 1995). This is the wet season for most sections of the islands and January precipitation patterns are frequently dominated by synoptic scale weather influences and trade wind showers. Trade wind related precipitation is a major source of precipitation across most of the state in January. Trade winds were generally weak or absent throughout January 1998 and few synoptic scale systems affected the islands. This weather pattern resulted in the very low rainfall totals. Kauai: All reporting stations had below average precipitation for the month. The most negative anomalous precipitation pattern in the month of January occurred on the south and southwest sides of the island with only 25 to 35 percent of average rainfall in those areas. Anahola and Lihue located on the east side of the island did approach average precipitation amount for the month, from a stalled frontal system (shear line)that pushed across the island early in the month. Oahu: Below average precipitation was observed during the month at all reporting stations due to less moisture tracking southwest in the trades, weak trade wind flow and fewer or weaker than average synoptic scale systems passing the islands. The greatest negative anomaly in January, was the central and southwest sections where frontal systems normally pass in January producing significant precipitation. The greatest negative precipitation anomaly in the central and along the southwest side of the island, the area known as the Waianae area (leeward of the Waianae Mountain range) where only 1 to 20 percent of average (.09 to .1.95 inches) precipitation occurred. Areas that are considered the wettest section of the island, the central Koolau Mountains, including the stations reporting at Wilson Tunnel and Manoa Lyons Arboretum were also below average, but with 6.53 and 6.29 inches (56 and 48 percent of average) reported respectively. Maui County: Molokai and Lanai were below average at reporting stations, with Lanai City receiving 32 percent of average rainfall (1.94 inches). The Island of Maui reporting stations indicated below average precipitation at all locations. Negative anomalies were particularly noted in the areas with dependence on synoptic scale precipitation in January, such as Lahainaluna, Kihei and Ulupalakua. This continues the several months period of very dry conditions in those areas. 5 to 46 percent of average rainfall occurred in those areas this month with rainfall amounts of .64 at Kihei to 2.39 at Ulupalakua. The running eight months rainfall total for Kihei has only been 1.74inches of rainfall which is 8.1 inches below average. Hawaii County: An extremely dry precipitation pattern was noted on the Big Island with all areas having well below average precipitation. This again is likely due to the decreased frequency of synoptic scale weather pattern days and possibly due to weaker or drier than average trade winds this month. The Kona side of the island, dependent on convective precipitation and this time of year synoptic scale precipitation patterns, was well came in with below average at all reporting locations. Kainalui (upslope of Kona town) was the station with the greatest negative precipitation anomaly with only 20 percent of average rainfall, 1.09 inches. Again, this is due to weak or drier than average synoptic scale weather systems. The following are rainfall statistics for selected locations around the state and comparative data from recent years and significant El Nino events. The island and station name are listed with the January 1998 rainfall total. For comparison, the average for the month and percent of average is listed for the station in the following two columns. Longer term statistics for hydrologic purposes are listed with November, December and January three month rainfall accumulations and the average for those three months in columns five and six. The final three columns are comparative data to past El Nino years rainfall from these sites or nearby National Weather Service recording stations. (LT = Long Term; units: inches) LT Pct 1997-98 LT Other El Nino Jan98 Ave LT Ave Nov-Jan Ave Jan94 Jan87 Jan83 Kauai--- Lihue 5.57 5.90 94 10.56 16.50 3.99 1.35 0.87 Hanalei 4.97 11.30 44 16.59 33.20 6.12 1.93 5.30 Hanapepe 1.56 5.00 31 3.63 12.50 1.19 0.25 0.40 Oahu--- Honolulu 0.77 3.60 21 2.05 10.40 0.78 0.42 0.32 Waianae 0.72 10.70 19 1.59 9.10 0.45 0.22 0.47 Hawaii Kai 1.44 4.60 31 4.73 11.70 2.46 1.50 m Manoa Lyon A. 6.29 13.20 48 32.86 41.00 15.70 7.38 4.01 Waialua 2.02 5.60 36 5.08 14.80 1.79 2.20 3.87 Ahuimanu 5.97 12.40 48 23.20 33.20 13.51 3.00 m (windward) Molokai--- Kaunakakai 1.69 3.30 51 3.31 7.90 0.21 2.00 2.30 Lanai--- Lanai City 1.94 6.10 32 8.96 14.50 1.47 1.57 1.18 Maui--- Kahului 0.36 4.10 09 5.21 9.90 1.12 2.91 0.58 Hana 0.73 9.50 08 7.78 24.30 10.90 7.29 2.69 Kihei 0.64 4.10 16 1.57 8.00 0.56 1.34 0.28 Lahainaluna 0.21 4.40 05 1.59 9.80 m 0.51 0.06 Wailuku 0.55 5.20 11 8.56 12.40 2.94 5.59 0.94 Hawaii--- Hilo 0.14* 9.90 01 17.10 25.60 10.39 9.02 0.90 Pahala 0.15 7.70 02 2.54 18.60 3.13 m 1.65 Honaunau (CC) 0.82 3.70 22 3.22 10.40 1.56 0.40 1.08 Kamuela 1.74 6.60 26 20.14 19.70 5.83 3.71 0.24 Laupahoehoe 0.36 13.50 03 22.73 41.90 21.18 13.42 1.99 *Lowest monthly rainfall amount ever recorded since record keeping begin. Data Sources: First order climate network weather observations stations of the National Weather Service at Lihue, HI, Honolulu, HI, Kahalui, HI, Hilo, HI. Additional data was taken from the HYDRONET state network of automated rain gages. Data collected in the automated gages are not certified and information used above should be used for information purposes only. Reference: Chu, Pao-Shin, 1995: Hawaii Rainfall Anomalies and El Nino, Journal of Climate, Vol 8, No.6, American Meteorological Society, June 1995. Roger V. Pierce, Senior Service Hydrologist National Weather Service Forecast Office Honolulu, Hawaii