MONTHLY PRECIPITATION SUMMARY State of Hawaii portion of Honolulu HSA MONTH: December 1998 PREPARED: January 4, 1999 State: No Flash Flood Warnings were issued for the state in December. Urban and Small Stream Flood Advisories were issued for portions of windward Oahu and Maui County on 28 Dec. The period from 1 to 13 December was marked by very strong trade winds that brought frequent but short-lived showers to the windward sections of the island chain. These showers also arrived within the remnants of old shear lines. An abrupt change of weather pattern occurred on 15 December with the passage of the first cold front of the 1998-99 cool season. This front was the first of three to push across the island chain during the month. The second and third frontal passages occurred on 28 December and 30-31 December, respectively. All three fronts brought showers to the islands but did not cause significant rain-related problems. The late start to the 1998-99 cool season rains combined with the lack of rain caused by the El- Nino episode during the first half of the year resulted in most gages across the state having annual totals below normal. Island of Kauai: The site at Wainiha was the only location to report higher than normal rainfall (11.71 inches, 105 percent of normal). The Hanalei gage was only slightly below normal with 9.09 inches, which is 94 percent of normal. Both gages are located along north facing slopes of the island and received most of their rain from showers carried by the strong trades during the first two weeks of the month and during the third frontal passage on 30 December. The rest of the gages reported amounts about 40 to 80 percent of normal. Island of Oahu: Rainfall from the frontal passages at the end of the month helped bring some relief to the dry leeward sections of the island. The Lualualei gage observed 2.41 inches of rain with a cold front passage on 31 December to bring the total for the month up to 2.89 inches (76 percent of normal). Many windward Oahu gages reported totals between 70 and 85 percent of normal. The Maunawili gage reported 10.21 inches, or 112 percent of normal. Most of this rain occurred during the period of strong trades across the state. Once again, the Manoa Lyon Arboretum topped all rain totals with 11.62 inches for December (81 percent of normal). December also brought to a close a very dry year for the Honolulu Airport site. The annual total of 4.52 inches broke an all-time record for low rainfall at that location (period of record 1947 to present). The previous record of 5.03 inches was set in 1983, which was also the tail end of a very strong El-Nino episode. However, a major caveat is attached to this year's record. On 31 December, a line of showers ahead of a cold front dropped 0.84 inches of rain between midnight and 5:00 AM HST. The ASOS site that takes these measurements subsequently failed and was out of service from 5:00 AM to about 4:30 PM HST. Rainfall did occur at the Honolulu Airport during this outage period, but backup observations did not note the rainfall to be of heavy intensity with a significant restriction to visibility. Another gage at Hickam Air Force Base, about 1.5 NM away, reported 0.51 inches for the entire day. Maui County: December was quite wet for West Maui. Both sites along the windward sections of West Maui (Kahakuloa, 6.10 inches, 117 percent of normal; and Wailuku, 4.34 inches, 101 percent of normal) reported higher than normal rainfall totals. As was the case with Oahu, the dry leeward sides of Maui saw some relief with the rainfall associated with the cold fronts. The gage at Kihei recorded 1.68 inches on 31 December to bring the month's total up to 1.82 inches, or 76 percent of normal. However, rainfall for all of 1998 remained very low at 2.62 inches, or only 17 percent of normal. Hawaii County: Persistent and strong trades during the first two weeks of December brought ample amounts of rainfall to the windward sections of the island with many sites reporting amounts greater than 75 percent of normal. Noteworthy sites include Mountain View, with 17.84 inches, or 110 percent of normal, and Glenwood, with 20.66 inches, or 120 percent of normal. Gages in Kona, Kau, and South Kohala continue to indicate a rainfall deficit with Pahala reporting 0.74 inches (14 percent of normal) and Kamakoa reporting only 0.05 inches, or 2 percent of normal. BELOW ARE RAINFALL STATISTICS FOR SELECTED LOCATIONS FROM AROUND THE STATE. THE FIRST COLUMN IS THE OBSERVED RAINFALL FOR DECEMBER. THE SECOND COLUMN IS THE 30 YEAR AVERAGE FOR THAT LOCATION WHILE THE THIRD COLUMN LISTS THE PERCENT OF AVERAGE RAINFALL FOR THE MONTH OF DECEMBER. KAUAI DEC AVG %AVG LIHUE 2.16 5.2 42 HANALEI 9.09 9.7 94 HANAPEPE 3.37 4.3 78 OAHU HONOLULU 1.15 3.8 30 MANOA ARBOR. 11.62 14.3 81 HAWAII KAI 1.76 4.1 43 AHUIMANU 7.02 10.9 64 WAIANAE 0.58 3.3 18 WAIALUA 4.08 5.0 82 MOLOKAI KAUNAKAKAI 1.25 3.0 42 LANAI LANAI CITY 2.28 4.6 50 MAUI KAHULUI 1.16 3.2 36 HANA 2.05 6.1 34 KIHEI 1.82 2.4 76 LAHAINALUNA 1.57 3.4 46 WAILUKU 4.34 4.3 101 HAWAII HILO 9.89 12.0 82 PAHALA 0.74 5.4 14 HONAUNAU 1.27 3.1 41 KAMUELA (UPPER) 2.91 6.0 49 KAMUELA 1.03 7.3 14 LAUPAHOEHOE 9.78 14.8 66 Data Sources: First order climate network weather observation stations of the National Weather Service at Lihue, HI, Honolulu, HI, Kahului, HI, and Hilo, HI. Additional data were 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. Kevin R. Kodama, Senior Service Hydrologist National Weather Service Forecast Office Honolulu, Hawaii