| Current Conditions | ||
| Temp |  | -1.5 C |
| RH | | 89 % |
| Wind | | SE 6 mph |
| Road | | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 963 FXHW60 PHFO 181351 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 351 AM HST Mon Nov 18 2019 .SYNOPSIS... An unsettled weather pattern will persist across the island chain through Tuesday, with locally heavy rainfall and thunderstorms possible statewide. The airmass will stabilize Tuesday night and Wednesday, but a showery wet trade wind pattern is expected to hold through the weekend. Breezy to windy conditions are expected Thursday through Saturday. && .DISCUSSION... Currently at the surface, a 1026 mb high centered around 1200 miles north-northeast of Honolulu is driving moderate trade winds in unsheltered areas across the island chain early this morning. Infrared satellite imagery shows partly cloudy conditions in most areas, with mostly cloudy skies in a few windward locales. Radar imagery shows scattered showers across Kauai and the Big Island, with isolated showers or rain free conditions elsewhere. Water Vapor imagery shows a closed upper level low spinning around 100 miles northeast of Kauai, and it is this feature that will keep unsettled conditions in place through the first half of the work week. Main short term concern revolves around the potential for heavy rainfall and thunderstorms over the next couple days. Moderate trade winds are expected to hold in place today, before easing into the light to moderate range tonight through Tuesday night as a new front approaches from the northwest. Model guidance is in good agreement showing the trades strengthening Wednesday and Wednesday night, with breezy to windy conditions expected Thursday into next weekend. The moist unstable airmass will linger over the state through at least Tuesday, as the upper level low moves slowly southwestward and over the western islands. Unsettled conditions, including the possibility for locally heavy rainfall and thunderstorms, will continue through Tuesday. A Flash Flood Watch remains in effect for the entire state through 6 PM today. The watch may need to be extended into Tuesday for all or portions of the island chain, but confidence is not high enough to extend the watch at this time. Models indicate that the upper low will open into a trough Tuesday night, then linger over the state through the remainder of the week. As a result, we should see conditions stabilize a touch beginning Tuesday night, but a showery wet trade wind pattern will likely continue into next weekend. && .AVIATION... The potential for heavy showers and a few thunderstorms will remain in the forecast today due to an upper low that has drifted into the area. Although clouds and showers will be most active over north and northeast facing slopes with the moderate trades in place, some will manage to spill over into leeward areas periodically. Trades will gradually trend down later today through tonight with light and variable winds possibly returning for Oahu and Kauai by Tuesday morning. MVFR conditions are possible in and around showers. AIRMET Sierra for mountain obscuration remains in effect over the Big Island and may be needed elsewhere as conditions evolve through the day. && .MARINE... The current northwest swell will continue to subside and the High Surf Advisory (HSA) has been cancelled. A small north-northwest swell is expected to fill in late Monday and peak Tuesday well below HSA levels. Currently in the north Pacific, we have a captured fetch of strong gales with pockets of storm force winds near 40N 170E that is traveling along the great circle route toward Hawaii. A large west-northwest to northwest swell should build throughout the day Wednesday and peak Wednesday night into Thursday at solid advisory levels and possibly warning levels for north and west facing shores of the smaller islands. The combination of a surface trough near the Big Island moving west slowly, and a disturbance aloft will continue to bring the threat of thunderstorms through Tuesday. The current Small Craft Advisory (SCA) for the typical windy zones around Maui County and the Big Island should be cancelled sometime this afternoon as winds drop below SCA speeds. Winds will ramp back up to SCA levels towards the middle of the week as high pressure strengthens north of the area. Winds may reach gale force by the end of the week across the typical windy zones of Maui County and the Big Island, with SCA level winds expected elsewhere. Overnight ASCAT pass revealed pockets of strong northeast winds upstream of the state. This may bring a slight uptick in surf along east facing shores today. The surf will increase further along east facing shores during the second half of the week as the trades become more robust. Expect choppy surf to increase along east facing shores with surf heights possibly nearing advisory levels this coming weekend. Minimal background swells are expected along south facing shores through most of the week with a few tiny southwest swells possible near the middle of the week. && .HFO WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through this afternoon for all Hawaii islands. Small Craft Advisory until 6 PM HST this evening for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Jelsema AVIATION...Gibbs MARINE...Kino Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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