131 FXHW60 PHFO 150213 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 413 PM HST Wed Feb 14 2018 .SYNOPSIS... A trough, at the surface and aloft, will persist near the islands through at least the beginning of next week. The trough will bring muggy, rainy weather. A front over Molokai will move slowly east through Friday night with drier weather over Kauai and Oahu and wetter weather for Maui County and the Big Island. Over the weekend, the rain band may spread back west over Oahu and possibly Kauai. && .DISCUSSION... Satellite loops show a low about 560 miles northwest of Oahu with a trough extending from the low to near Kauai. Winds near the surface are from the southeast near the Big Island of Hawaii, veering to southwest near Kauai. The low is making the atmosphere over the islands unstable while very moist air is moving up over the area from the southeast. A front over Molokai is moving southeast slowly. There is a band of heavy showers and isolated thunderstorms along the front. One shower after another is moving along the band from the south southwest producing heavy rain over Molokai. Behind the front, shallow gentle west winds have brought drier weather to Oahu and Kauai. Ahead of the front, the weather is relatively quiet on the Big Island of Hawaii, with cloudy skies over the lower slopes but only light rainfall. The shower band over Molokai is expected to continue moving slowly southeast across Maui County tonight and over the Big Island by tomorrow. A Flash Flood Watch is in effect for Maui County and the Big Island for heavy rainfall from the front. The Band may linger over the Big Island through the weekend. Temperatures will be cooling aloft by the weekend, so chances of snow on the summits of Mauna Kea and Mauna Loa will increase. The forecast becomes more uncertain beyond the weekend, but the global models suggest a new low will form northwest of the area and move toward the islands early next week. As the new low approaches, the shower band may spread back westward. By the middle of next week, a ridge may build northeast of the islands with trade winds possibly returning for the second half of next week. $$ .MARINE... Winds should be on the decline this evening over the eastern half of the coastal waters, as the front weakens and pushes E, weakening the pressure gradient near Maui county and the Big Island. Did not get a good mid-morning ASCAT pass but based on the downward trend in the guidance this evening, will cancel the Small Craft Advisory at 4 pm. A general trend toward weakening winds (especially over the eastern half of the coastal waters) is expected over the next day or so as a weak front or surface trough shifts toward Maui and the Big Island for Thu into Fri. The trough should weaken enough over the weekend for northerlies to increase near the Kauai waters and southeasterlies to increase over the eastern waters. Seas will also continue to decline as the quick WNW swell pulse fades. A storm-force low pressure approaching the dateline at 48N will only briefly have a short fetch window aimed at us, providing as us sub-advisory level NW pulse this weekend. A very large surface high far to our NE, with 15-25 kt trades over a wide fetch over the eastern Pacific, will keep short period surf going on eastern shores for the next few days. Instability and deep layer shear appear to be more than sufficient through the next 12 to 24 hours for some thunderstorms to become strong to severe, especially over the coastal waters N of Maui county and the Big Island, extending out into the adjacent offshore waters. && AVIATION... A cold front over Molokai is slowly pushing SE with a low pressure center well to the NW of the island chain. The low will push to the SE then shift to the east on Thursday morning remaining a few hundred miles north of Kauai. Shower activity associated with the front has a history of embedded heavy rain and thunderstorms. This is now tracking across Molokai and should affect Lanai this afternoon and Maui later this afternoon into the evening hours. Layered clouds associated with this cloud band has the potential for light ice. Periods of MVFR to IFR conditions can be expected with the embedded heavier rain. AIRMET SIERRA for MTN OBSC is posted over Oahu and Molokai and may need to be expanded over Maui tonight. A trough aloft is producing some turbulence, so AIRMET TANGO is in effect for moderate turbulence aloft. && $$ DISCUSSION...Donaldson MARINE...R Ballard AVIATION...Chevalier/Eaton