MONTHLY PRECIPITATION SUMMARY Hawaiian Islands MONTH: April 1998 PREPARED May 1, 1998 State:No significant Flash flooding was reported. Significant drought conditions continue across the state. Below average precipitation occurred state wide with all first order and 58 automated rain gages receiving less than average rainfall in April. Hawaii has four first order National Weather Service Offices and 69 automated rain gage stations. This continued the seven month trend state wide of drier than usual conditions. A major consideration in things returning to closer to average conditions is that April is the end of the wet season and average rainfalls in many locations on the islands go below 1 inch per month. During much of April 1998, a ridge of high pressure that had been over and west of the islands shifted north of the islands at all levels of the atmosphere. This allowed the surface high northeast of the islands to strengthen to nearer to average position and strength. This shift in weather patterns came with the shift to the spring season and has brought stronger trade winds and thus trade wind showers to the windward sides of the islands. This added rainfall in windward areas has helped relieve some of the very dry conditions there. However, much more rainfall is needed to get beyond the longer term drought situation. Island of Kauai: Most reporting stations had just at or below average precipitation for the month. The most negative anomalous precipitation pattern in the month of March occurred on the north and northeast sides of the island with only 33 to 72 percent of average rainfall in those areas. Kokee on the northwest side of the island received the greatest amount of precipitation for the month, 12.04 inches which was 177 percent of average. This is one of the favored locations for trade wind showers with winds blowing just a little east of northeast. The south side of the island received significant rainfalls this month mainly from being in the favored location for trade winds blowing around the south side of Mt. Waialeale. Island of Oahu: Below average precipitation again occurred this month at most locations. Areas in the central portion of the island were the exception with above average rainfall. Trade wind showers that developed on the Koolau mountains moved on down wind to the west southwest depositing significant rainfall in the central portions of the island and on the northeast facing sections of the Waianae mountains. Leeward areas were again below average as frontal systems that pass through or near the islands at times in April did not materialize. The greatest negative precipitation anomaly was along the southwest side of the island, in the area known as the Waianae area (leeward of the Waianae Mountain range) where only 14 percent of average (.23 inches) precipitation occurred. Even though rainfall did increase in windward areas, most locations still were below average as this is one of the wetter months of the year. Maui County: Molokai and Lanai were below average at reporting stations with Lanai City receiving 61 percent of average rainfall (2.13 inches). The Island of Maui reporting stations indicated below average precipitation at all but one location. Negative anomalies were particularly noted in the areas with dependence on synoptic scale precipitation in April, such as Lahainaluna, Kihei and Ulupalakua. This continues the several months' period of very dry conditions in those areas. Zero to 42 percent of average rainfall occurred in those areas this month with rainfall amounts of 0.00 at Kihei to 0.71 at Lahaninaluna. The running nine months' rainfall total for Kihei has only been 1.83 inches, which is 12.9 inches below average. Hawaii County: A wetter precipitation pattern was noted on the Big Island with all windward areas coming much closer to average precipitation than in previous months. This is one of the areas where the return of trade winds and showers were significant in helping relieve some of the drier conditions in the state. The areas in the Kohala mountains, have not suffered as greatly from dry conditions through the winter, received well above average rainfall in April. It appears as though when the trade winds are a little east of the average trade wind direction, which appears to have occurred frequently in April, this area is favored for precipitation. The Kina side of the island starts becoming more dependent on convective precipitation at this time of year. Weather patterns didn't favor afternoon convection and a good set up of sea breezes in those areas and precipitation was well below average at all reporting locations in those areas. Waiaha, not far from and up slope of Kailua - Kona Town, was the station with the greatest negative precipitation anomaly with only 25 percent of average or 1.59 inches of rainfall. Below are statistics and part of a Public Information Station. THE FOLLOWING ARE RAINFALL STATISTICS FOR SELECTED LOCATIONS AROUND THE STATE AND COMPARATIVE DATA. THE ISLAND AND STATION NAME ARE LISTED WITH THE MAY 1998 RAINFALL TOTAL. FOR COMPARISON... THE AVERAGE FOR THE MONTH AND PERCENT OF AVERAGE ARE LISTED FOR THE STATION IN THE FOLLOWING TWO COLUMNS. LONGER TERM STATISTICS ARE LISTED WITH FEBRUARY... MARCH AND APRIL THREE MONTH RAINFALL ACCUMULATIONS... AVERAGES FOR THOSE THREE MONTHS AND PERCENT OF AVERAGE FOR THE THREE IN COLUMNS FIVE... SIX AND SEVEN. Data units are inches. Kauai Apr 98 Ave Pct Ave Feb-Mar-Apr Ave Pct Ave Lihue 1.83 3.50 52 4.34 11.00 39 Hanalei 8.07 12.70 64 14.51 36.80 42 Hanapepe 2.84 2.20 129 3.77 8.40 45 Oahu Honolulu 0.54 1.50 36 0.78 5.91 13 Waianae 0.23 1.60 14 0.38 6.40 6 Hawaii Kai 0.45 2.20 20 1.49 9.30 16 Manoa Lyon A. 12.06 13.00 93 20.46 37.60 54 Waialua 1.08 2.80 39 1.96 10.50 19 Ahuimanu 3.12 9.90 39 7.78 23.50 33 Molokai Kaunakakai 0.19 1.20 16 1.01 5.60 18 Lanai Lanai City 2.13 3.50 61 4.88 11.30 43 Maui Kahului 0.97 1.80 54 1.64 7.40 22 Hana 2.33 9.00 26 3.96 25.30 16 Kihei 0.00 1.20 0 0.09 5.50 2 Lahainaluna 0.71 1.70 42 1.16 6.80 17 Wailuku 1.44 3.00 48 5.24 13.60 39 Hawaii Hilo 8.86 15.30 58 18.34 39.50 46 Pahala 0.43 5.00 9 0.82 17.40 5 Honaunau (Captain Cook 2.12 6.10 55 4.02 14.40 28 Kamuela 14.26 6.90 207 20.10 20.80 97 Kamuela (Higher Elev.) 16.59 6.90 240 24.90 18.70 133 Laupahoehoe 14.62 18.90 77 23.72 51.60 46 Sources: First order climate network weather observations stations of the National Weather Service at Lihue, HI, Honolulu, HI, Kahalui, HI, 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. Roger V. Pierce, Senior Service Hydrologist National Weather Service Forecast Office Honolulu, Hawaii