| Current Conditions | ||
| Temp |  | 4.4 C |
| RH | | 12 % |
| Wind | | NNE 20 mph |
| Road | | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 045 FXHW60 PHFO 180655 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 855 PM HST Sat Aug 17 2019 .SYNOPSIS... The ridge of high pressure north of the Hawaiian Islands will weaken through Sunday night, resulting in lighter trades the next couple of days. Locally strong trades will return by the middle of next week as the ridge of high pressure ridge rebuilds north of the area. Showers riding in with the trades will favor the windward and mountain areas, especially during the nights and early mornings. Rainfall amounts, though, will be light. && .DISCUSSION... The mainly moderate trades blowing this evening will be trending lighter through Sunday night as the ridge of high pressure located 420 miles north of Kauai weakens. It appears Monday will have the lightest winds. With the lighter trades, expect daytime sea- breeze to arise, especially along the lee and interior areas of the smaller islands. This will lead to some afternoon clouds over these areas, but not a whole lot of showers are expected from them as a mid level ridge will limit their vertical extent to no higher than 10k feet on both Sunday and Monday afternoons, meaning isolated and spotty at best. Leeward Big Island will get their usual afternoon and evening clouds each day with only isolated to scattered showers at best from these clouds. A disturbance passing south of the islands Tuesday night into Wednesday may bring some added trade wind moisture to especially the eastern islands. But otherwise, this rather dry trade wind pattern will continue. A boost in the trades will commence as early as Monday night, building to moderate to locally strong by Wednesday. This locally strong trade wind regime will hold through the second half of next week with a 1025 mb surface high sitting far north of the islands. && .AVIATION... A ridge of high pressure north of the state will keep moderate trade winds in place through Sunday. Low clouds and showers will bring brief MVFR cigs/vsbys to windward and mauka areas, mainly during the overnight and early morning hours. Predominantly VFR conditions are expected during the next 24 hours. No AIRMETs are currently in effect. && .MARINE... Trades are forecast to weaken into the light to moderate category Sunday through Monday as the gradient relaxes over the state. Localized land breezes through the overnight and early morning periods followed by late morning and afternoon sea breezes will be possible near the coasts through this time. Guidance remains in good agreement Tuesday through the second half of the week and depicts a strengthening ridge north of the islands, which supports a return of fresh to locally strong trades (advisory-level winds in the typically windier locations between Maui County and the Big Island) by Wednesday. Surf along south facing shores will remain small through Monday, with mainly background energy continuing out of the southwest and southeast. An upward trend is anticipated beginning Monday night, as one of the largest south swells of the season begins to build across the Hawaiian waters. Surface analysis charts showed a compact storm-force low bottoming out at 956 mb southeast of New Zealand last Monday through Tuesday within Hawaii's swell window. ASCAT passes reflected this and showed a pocket of storm-force winds nosing northward through this period within the 190-200 deg bands relative to the islands. Altimeter passes within this area showed seas ranging from 35 to 42 ft. This swell has already moved through the nearshore PacIOOS buoy at Pago Pago, which showed seas slightly higher than predicted by guidance. Energy levels within the lower frequency bands closely resembled the levels observed at this buoy for our recent July 14th warning-level event. As a result, surf heights will likely near/reach warning levels along south facing shores through the peak of the event Tuesday through Tuesday night and may not drop below advisory levels until Thursday. The small westerly swell associated with recent typhoon activity in the western Pacific will steadily trend down Sunday through Monday. Surf will respond and lower along the exposed coasts from this source. Surf along north and west facing shores may slightly trend up through the second half of the week as a small northwest swell builds down the island chain. Guidance remains in good agreement and depicts a gale evolving around 2000 miles northwest of the islands near and just west of the Date Line early this week. Surf along east facing shores will trend up by midweek as the trades strengthen locally and upstream of the islands. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ H Lau...Jelsema...Gibbs Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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