Current Conditions | ||
Temp | ![]() | -1.0 C |
RH | ![]() | 100 % |
Wind | ![]() | N 16 mph |
Road | ![]() | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 864 FXHW60 PHFO 260138 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 338 PM HST Mon Jan 25 2021 .SYNOPSIS... Locally breezy east to southeast winds and wet conditions with heavy showers and the potential for flash flooding will persist through Tuesday. Showers will diminish from east to west on Wednesday. Breezy trade winds and will focus showers over windward areas from Thursday through the weekend. && .DISCUSSION... The deep moisture and heavy showers that have been focused along windward and southeast slopes of the Big Island have spread to other islands this afternoon. Strong high pressure centered about 1,300 miles northeast of the state and a deep trough several hundred miles to the west of the islands are causing the breezy winds to shift out of the east to southeast. The deep trough is also producing a broad area of convergence, and the islands sit along the northern fringe of this area of heavy showers and thunderstorms. This feature has dropped 5 to 7 inches of rainfall over the Kau, Puna, and Hilo Districts of the Big Island during the past 12 hours, and heavy rainfall has developed over and around Oahu and Kauai this afternoon. As a result, the Flash Flood Watch has been expanded from the Big Island to cover the entire state. While the primary threat will be over windward areas, anywhere may experience flash flooding. Also, a Winter Storm Warning is up for the high summits of the Big Island. The weather pattern will change little tonight and Tuesday. The low-level flow will remain out of the east to southeast, and the islands will remains along the north edge of the deep moisture. The GFS model is hinting at a developing area of divergence aloft that could shift the highest chance for heavy showers around Kauai and Oahu. Windward areas should experience more rainfall, but the Flash Flood Watch is out for all areas of the state through Tuesday afternoon. The threat for heavy rainfall is expected to diminish from east to west on Wednesday and Wednesday night. The GFS and ECMWF models show the mid- to upper-level trough southwest of the state filling, which should allow the area of moisture convergence to slowly move off to the west. Meanwhile, the surface high to the northeast will only weaken slightly, leading to breezy and gusty trade winds. As a result, showers, some heavy, will be focused over windward slopes, with some occasionally spreading to leeward areas of the smaller islands. Breezy trade wind weather will prevail Thursday through the weekend. A mid-level ridge will lead to more stable conditions, and showers will be focused over typical windward slopes. Although timing varies, the GFS and ECMWF are showing a band of enhanced trade wind showers moving through Friday or Friday night. && .AVIATION... A temporary window of improving conditions is currently observed over windward Big Island while widespread persistent MVFR is noted for remaining windward areas. Likewise, moderate to locally heavy rain has, for the most part, been focused over windward areas. The exception has been Oahu where the Lanai and Molokai plumes are both in full swing bringing steady moderate rainfall and episodic IFR/localized LIFR within the heaviest showers. Radar trends suggest this activity will persist over Oahu, including PHNL, for at least a couple more hours. Further, this corridor of activity is now advancing northwest of Oahu and is forecast to reach the eastern and southern slopes of Kauai, including PHLI, by around 04z/6pm HST. Additional moisture immediately upstream of the Islands, and now apparent on regional radar imagery, will move into the area tonight and will support a continued threat of locally heavy rain and MVFR/localized IFR conditions, chiefly over windward areas. AIRMET Sierra remains in effect for windward mountain obscuration for Big Island through Kauai. A forthcoming update will expand the AIRMET over Oahu to include the entire island. AIRMET Tango remains in effect for low-level mechanical turb and strong surface winds over some adjacent coastal waters. AIRMET Zulu remains in effect for moderate rime icing over Big Island and adj waters to the east. These conditions will remain in place through today and possibly through tonight. && .MARINE... Robust high pressure far north and northeast of the islands will sustain breezy to strong east and southeast winds across local waters through the week. Thus, a Small Craft Advisory remains in effect for winds (at or above 25 knots) and/or seas (at or above 10 ft) across exposed waters. Surf along east facing shores will remain rough due to the strong onshore winds locally and upstream across the eastern Pacific, driving large seas through the area. The advisory in place will likely become extended into Wednesday. A slightly downward trend will be possible through the second half of the week as the upstream fetch diminishes across the eastern Pacific. Surf along north and west facing shores will steadily lower through tonight as a northwest swell eases. A large scale pattern change across the Pacific over the past week featuring a blocking pattern setting up east of the date line will translate to an end of the active run of large swells that began in the second half of December and continued through the first half of January. Surf will respond and drop well below the January average Tuesday through midweek. For the long range, guidance shows a developing hurricane-force low far northwest of Hawaii, tracking northward toward the western Aleutians through Tuesday. Wave models reflect this and show small, long-period energy arriving through the day Thursday out of the west-northwest, then trending up out of the northwest Friday into the weekend. Large errors typically associated with these sources lead to low forecast confidence, however. Surf along south facing shores will trend up through midweek, as an out-of-season Tasman source arrives. Surf should drop and return to normal levels through the second half of the week. && .HFO WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through Tuesday afternoon for all Hawaii islands. High Surf Advisory until 6 PM HST Tuesday for Kauai Windward- Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward Haleakala-Big Island North and East. Winter Storm Warning until 6 PM HST Tuesday for Big Island Summits. Small Craft Advisory until 6 PM HST Wednesday for all Hawaiian waters. && $$ DISCUSSION...Wroe AVIATION...JVC MARINE...Kinel Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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