| Current Conditions | ||
| Temp |  | 7.9 C |
| RH | | 53 % |
| Wind | | SSE 20 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 733 FXHW60 PHFO 241957 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 957 AM HST Mon Jun 24 2019 .SYNOPSIS... A low, at the surface and aloft, will persist northwest of the islands through Thursday. The low will dissipate over the second half of the week as a high builds northeast of the area. && .DISCUSSION... The heavy showers and thunderstorms that affected the main Hawaiian Islands yesterday have dissipated. Satellite loops show mostly cloudy skies over Oahu and Maui County and partly sunny skies over the Big Island and Kauai. The weather is mostly dry over the Big Island, Maui County and Kauai with scattered light to moderate showers moving over Oahu and Niihau. The weather pattern in the north central Pacific remains very unusual for late June. A 1010 mb surface low is nearly stationary 915 miles northwest of Kauai near 31N171W and a front associated with the low runs from 30N161W to 200 miles northwest of Kauai to 21N164W. A 1026 mb surface high is far northwest of the islands near 37N139W with a ridge extending from the high over Maui County. South of the ridge, moderate to locally fresh easterly trade winds are blowing near the Big Island. The surface winds veer out of the southeast around the smaller islands. Southeast flow over the islands will be partly blocked by the Big Island, so winds will be gentle and variable over the smaller islands with daytime sea breezes and nighttime land breezes. Moisture and instability associated with the low and front west of the islands is expected to spread east starting tonight. The threat of heavy rain and thunderstorms will be greatest over Kauai County tonight, but the computer models show this threat spreading over Oahu on Tuesday and possibly reaching Maui County. A Flash Flood Watch remains in effect for Kauai County and Oahu. We may need to expand the watch to include Maui County. The atmosphere over the Big Island will be drier and more stable, but afternoon heating could produce spotty heavy showers or even isolated thunderstorms over the Big Island slopes today. Moisture and instability over the islands will subside starting Wednesday night as the low weakens and high pressure builds northeast of the state. Trade winds will spread back over the islands starting Thursday evening bringing drier air and ending the threat of heavy showers. && .AVIATION... There is enough moisture and instability over Kauai that there should be rain, which could be heavy at times with the possibility of thunderstorms. Western portions of Oahu may be clipped by a few showers as well. Where we have the showers we are expecting lower level ceilings and possible mountain obscurations, mainly for Kauai and Oahu today. The rest of the state should see passing MVFR conditions with afternoon sea breezes and overnight land breezes with showers along the windward slopes possibly spilling over to a few interior sections this afternoon. AIRMET Sierra is currently in effect for Oahu for mountain obscurations above 2,000ft. Will monitor Kauai and issue an AIRMET for mountain obscuration if warranted. && .MARINE... Heavy showers and thunderstorms are increasingly likely from tonight Tuesday through Thursday, as a potent disturbance aloft approaches from the NW and supports the development of a slow- moving convergence band over portions of the area. Threats to mariners include locally gusty wind and reduced visibility in areas of heavy showers/thunderstorms, as well as dangerous cloud- to-surface lightning strikes, and the potential for waterspouts. The threat of unsettled weather will initially be greatest over waters around Kauai and Oahu from tonight into Tuesday, potentially spreading E to include Maui county waters later Tuesday into Wednesday. Unsettled weather is expected to continue over (at least) waters around Kauai and Oahu through Thursday, before the convergence band gradually moves away to the W Friday into Saturday. Outside areas of convection, expect moderate to locally fresh E to SE winds over Big Island waters, while the remainder of the waters can expect light to moderate SE to S winds that may occasionally shift SW. Seasonably strong trade winds will build over the area from the E Friday and Saturday. Until that time, winds and seas are expected to be below Small Craft Advisory criteria. Surf along all shores is expected to be below High Surf Advisory levels through the week, but a S swell arriving next weekend is expected to bring advisory-level surf to S facing shores. A small short-period NE swell will linger for another day or so before diminishing, while building trade winds next weekend will bring increasingly choppy surf to E facing shores. && .HFO WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch from 6 PM HST this evening through Wednesday afternoon for Niihau, Kauai and Oahu. && $$ DISCUSSION...Donaldson AVIATION...Chevalier MARINE...Birchard Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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