| Current Conditions | ||
| Temp |  | 2.5 C |
| RH | | 44 % |
| Wind | | NNE 3 mph |
| Road | | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 258 FXHW60 PHFO 170207 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 407 PM HST Tue Oct 16 2018 .SYNOPSIS... Moderate trades will slowly weaken through Friday, then strengthen again on Saturday. Remnants of a front will linger near the Big Island for the next few days. A trough aloft will bring somewhat unstable conditions around the Big Island before moving away late this week. Drier weather will persist for the western half of the state this week. && .DISCUSSION... Water vapor imagery shows a trough aloft over the western end of the state. A few high clouds are passing over the Big Island along the subtropical jet on the eastern flank of the trough. The trough aloft is also making the atmosphere less stable over the Big Island and isolated thunderstorms have popped up along the Kau District this afternoon. At the low levels of the atmosphere, a 1021 mb high about 900 miles north of Kauai near 35N 156W is moving east at 20 mph. The high is driving moderate trade winds across the state. Visible satellite shows showery low clouds, the remnants of a frontal band, extend upstream of Maui and the Big Island towards the east northeast. The trades are pushing these clouds and scattered showers across the windward slopes of both islands this afternoon. Fewer clouds and showers are tracking in with the trade winds across Molokai, Oahu and Kauai. The current weather pattern will remain unchanged through Wednesday as the remnant frontal clouds and upper trough remain in the same position. By Wednesday night, the high to the north begins to weaken and the trades will slowly taper off to gentle breezes by Friday. The trough aloft will slowly begin to move away to the northeast of the state Thursday and Friday, while the old frontal band shifts east of the Big Island resulting in a gradual drying trend for the windward slopes of Maui and the Big Island during the second half of the week. The trade winds are forecast to strengthen to moderate breezes again Saturday as another high builds in from the northwest. && .AVIATION... Moderate to fresh trade wind flow will continue tonight. These trade winds have carried the remnants of an old frontal boundary towards the islands. Expect shower activity to be focused along Windward slopes and coasts, especially those of the Big Island. Ceilings have risen slightly this afternoon, but are expected to drop again overnight. Occasional MVFR ceilings across Windward Big Island will likely become widespread by late evening. AIRMET Sierra for mountain obscuration will remain in effect for the north and east facing slopes of the Big Island. Sierra may need to be expanded to include eastern Maui late tonight. Elsewhere, across the remaining smaller islands, isolated MVFR ceilings and visibilities are to be expected in passing showers, but VFR conditions will predominate. Also, AIRMET Tango for moderate upper-level turbulence remains in effect over the island chain between FL280 and FL400 in association with a deep trough aloft passing close to the islands. Conditions are expected to end by this evening. && .MARINE... The current north-northwest swell continues to be on the rise this afternoon. A surge this morning at the near shore buoys was short lived, with the buoys quickly returning to the expected forecast rise. The swell is still rising at buoys 51001 and 51101 and is expected to peak there within the next few hours. This remains on track with the last couple model runs. The High Surf Advisory (HSA) remains in effect for north and some west facing shores of the smaller islands. Will continue to monitor should the swell peak higher requiring a warning, or if enough energy reaches the Big Island to require an advisory there. At this time, still looks like the Big Island will peak just below advisory levels. The swell is producing seas in excess of 10 feet over some waters, and combined with moderate to locally fresh trades, the Small Craft Advisory (SCA) remains in place for all waters except the leeward Maui County and leeward and southeast Big Island waters. The SCA and HSA are both in effect until 6pm Wednesday, but they may need to be extended depending on how the event pans out. Trades are expected to ease during the second half of the week. A smaller north-northwest swell is expected to arrive this weekend, but is expected to remain below advisory levels. Surf along south facing shores will remain elevated overnight, but remain below advisory levels, and then trend down Wednesday. A new south swell is expected to arrive Friday, and peak Saturday into Sunday at high end advisory or low end warning levels. See the latest collaborative surf discussion (SRDHFO) for more details. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 PM HST Wednesday for all coastal waters except Maui Leeward Waters, Big Island Waters and Big Island Southeast Waters. Small Craft Advisory until 6 PM HST Wednesday for north and west facing shores of Niihau, Kauai, Oahu and Molokai and north facing shores of Maui. && $$ DISCUSSION...Foster AVIATION...Bedal MARINE...M Ballard Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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