| Current Conditions | ||
| Temp |  | 8.4 C |
| RH | | 45 % |
| Wind | | SW 21 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 560 FXHW60 PHFO 250200 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 400 PM 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... Satellite loops show north to south bands of overcast, showery low clouds nearly stationary over Kauai County and Oahu. Radars show numerous moderate showers moving over Kauai County and Oahu from the south. There area partly sunny skies over Maui County and the Big Island with mostly dry weather. The weather pattern in the north central Pacific remains very unusual for late June. A 1008 mb surface low is nearly stationary 700 miles northwest of Kauai near 31N168W and a front associated with the low runs from 30N159W to 135 miles northwest of Kauai. A 1024 mb surface high is far northeast of the islands near 36N138W with a ridge extending from the high over Maui County. South of the ridge, moderate to locally fresh easterly trade winds are continuing to blow 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 tomorrow. 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. 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... Moisture and instability over Kauai will produce showers, which could be heavy at times with the possibility of thunderstorms for the remainder of Monday. 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 Monday evening. 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... A potent disturbance aloft will approach the islands from the NW through Tuesday, supporting the development of a closed low aloft several hundred miles NW of the islands. The low is expected to linger for a couple of days, supporting the development of one or more slow-moving convergence bands over portions of the area. The threat of unsettled weather will be greatest over waters around Kauai and Oahu through Thursday, potentially spreading E to include Maui county waters later Tuesday into Wednesday. Threats to mariners include locally erratic wind and reduced visibility in areas of heavy showers/thunderstorms, as well as the potential for cloud-to-surface lightning strikes and waterspouts. This system is not expected to bring impactful weather to Big Island waters. Outside areas of convection, expect moderate to locally fresh E to SE winds over Big Island waters, while the remainder of the waters will see light to moderate SE to S winds that may occasionally shift SW. If a weak surface low develops in response to the low aloft, S winds may briefly become fresh to strong near Kauai later in the week. As the low departs to the NW, and high pressure builds to the NE, E trade winds will build over the area 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 long-period 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 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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