MONTHLY PRECIPITATION SUMMARY State of Hawaii portion of Honolulu HSA MONTH: April 1999 PREPARED: May 11, 1999 State: Trade winds were uninterrupted through the month of April across the Hawaiian Islands. Strong trades destabilized by an upper level low just to the northeast of the island chain brought heavy showers to portions of the island of Hawaii during 10 to 13 April. An Urban and Small Stream Flood Advisory was issued on 11 and 13 April due to reports of minor flooding over the North and South Kona Districts (11 Apr) and the Hilo area (13 Apr) of that island. Following this rain event, the entire state experienced a general drying trend in light to moderate trades that persisted through the remainder of the month. Island of Kauai: For the third consecutive month, all sites across the island reported below normal totals. Persistent trades through the month resulted in the highest totals being observed at windward locations such as Hanalei (6.56 inches) and Wainiha (6.07 inches). However, these amounts are only about half of the April normal. Strong trade winds during the period from 10 to 13 April helped push rainfall into portions of the drier south-facing slopes. As a result, gages in the area (Omao and Kalaheo) reported totals around 70 percent of normal. Island of Oahu April was Oahu's best month of the 1998-99 cool season in terms of monthly rainfall. Seven sites, mainly along the slopes of the Koolau Range, reported higher than normal totals. These sites are Palisades, Waiawa, Moanalua, Kahuku, Luluku, Manoa Lyon, and Wheeler. For the Wheeler site, the total of 4.80 inches (109 percent of normal) was the highest amount observed in the last 12 months. The Mililani and Nuuanu gages were very close to normal at 91 percent (3.64 inches and 11.69 inches, respectively). Unfortunately for leeward locations, the persistent trades meant low rainfall totals. For instance, rainfall at Honolulu Airport was 45 percent of normal at 0.68 inches. The last time this site received a monthly rainfall total at or above normal was back in October 1997. Maui County Another dry month for the island of Maui with all gages reporting below normal rainfall. Conditions were especially dry over the leeward areas where all gages reported totals at less than 20 percent of normal. For the second consecutive month, the Kihei gage reported zero rainfall. The Waikapu Country Club site came close to matching Kihei with only 0.06 inches (2 percent of normal). Windward sites fared better under the sustained trade flow with Haiku reporting 4.43 inches (69 percent of normal) and Hana reporting 4.14 inches (46 percent of normal). For the Haiku site, most of the daily rainfall totals were distributed quite evenly during the period of wet trades from 5 to 12 April. Molokai remained dry with both sites reporting less than 25 percent of normal rainfall. Lanai City saw 2.91 inches (83 percent of normal), of which 1.01 inches fell during a 6-hour period on the morning of 12 April. Island of Hawaii: Wet trades over the windward areas ruled during the first half of April. Amounts were especially high in the South Hilo and Puna Districts where four out of six sites (Waiakea Uka, Mt. View, Glenwood, Hilo Airport) reported higher than normal rainfall. The other two sites, Piihonua and Pahoa, were close to normal at 91 percent. About 30 to 50 percent of the rain in the South Hilo and Puna District sites occurred during the period from 11 to 13 April when rain bands embedded within strong trade flow were enhanced by an upper level low northeast of the islands. For the Glenwood site, April marked the sixth consecutive month with rainfall over 20 inches and the thirteenth month of above normal rainfall. The Waiakea Uka gage just upslope from the city of Hilo has received more than 20 inches per month in seven of the last eight months. Conversely, many areas in the North and South Kona Districts remain dry. A few heavy showers did occur in the area during April, but these were highly localized, short-lived events. All four gages located in the Kona area reported below normal (33 to 53 percent) rainfall. The last time the Honaunau and Kealakekua sites reported rainfall at or above normal was in October 1997 and June 1997, respectively. THE FOLLOWING LIST CONTAINS RAINFALL STATISTICS FOR SELECTED LOCATIONS FROM AROUND THE STATE. THE FIRST COLUMN IS THE OBSERVED RAINFALL FOR APRIL. 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 APRIL. KAUAI APR AVG %AVG LIHUE AIRPORT 3.12 3.5 89 HANALEI 6.56 12.7 52 HANAPEPE 0.76 2.2 35 OAHU HONOLULU AIRPORT 0.68 1.5 45 MANOA ARBOR. 14.32 13.0 110 NIU VALLEY 0.85 4.0 21 WAIHEE PUMP 7.32 10.6 69 LUALUALEI 1.03 1.8 57 WAIALUA 1.70 2.8 61 MOLOKAI KAUNAKAKAI 0.15 1.2 13 LANAI LANAI CITY 2.91 3.5 83 MAUI KAHULUI AIRPORT 0.34 1.8 19 HANA 4.14 9.0 46 KIHEI 0.00 1.2 0 LAHAINALUNA 0.18 1.7 11 WAILUKU 0.32 3.0 11 HAWAII HILO AIRPORT 16.04 15.3 105 PAHALA 1.39 5.0 28 HONAUNAU 3.22 6.1 53 KAMUELA (UPPER) 2.71 6.9 39 GLENWOOD 21.42 17.2 125 LAUPAHOEHOE 10.67 18.9 56 Data Sources: First order climate network weather observation stations of the National Weather Service at Lihue, Honolulu, Kahului, 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