| Current Conditions | ||
| Temp |  | 3.6 C |
| RH | | 34 % |
| Wind | | WSW 13 mph |
| Road | | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 442 FXHW60 PHFO 130138 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 338 PM HST Tue Nov 12 2019 .SYNOPSIS... Light trade winds will prevail through tomorrow, then shift out of the south Thursday and Friday as a cold front advances toward the state. Light showers will favor the typical windward slopes into Thursday, though afternoon sea breezes may produce an isolated showers over interior sections. Rain chances will trend up this weekend as the front approaches the western end of the state and a weak trough moves in from the east. && .DISCUSSION... A stable and weak trade wind flow will persist through tomorrow. The subtropical ridge driving the trades remains weakened and displaced southward to about 225 miles north of Kauai, where it will generally remain through tomorrow. As a result, trades will be light enough to be overpowered by local overnight land breezes and afternoon sea breezes. Modest showers will favor windward slopes, while afternoon sea breezes produce clouds and a few showers over interior sections. A ridge aloft is producing rather stable conditions with a strengthening inversion noted in the afternoon soundings. For tonight, expect windward and north facing slopes of Kauai to experience scattered light showers, while little shower activity is anticipated elsewhere. Winds will gradually veer southerly on Thursday and Friday as a front advances toward the state. A somewhat dry and stable land and sea breeze pattern should persist on Thursday, with spotty afternoon showers favoring interior sections. Shower chances will increase on Friday over portions of the island chain. Expect prefrontal showers to develop ahead of the front near Kauai, and a trough moving in from the east may provide a boost to rainfall over the Big Island later in the day. Wetter, and possibly unsettled, conditions are expected during the weekend, though details remain somewhat uncertain. The front will stall and dissipate near Kauai, likely providing an increase in showers for the western end of the state. Meanwhile, moisture associated with the surface trough will spread westward, producing increased rain chances for the Big Island and Maui. An upper level trough will dig toward the state on Saturday and possibly form a cutoff low overhead on Sunday. This will likely destabilize the atmosphere and could lead to heavy showers and thunderstorms. Given uncertainty in the long range regarding the position and strength of the upper low, we have decided to hold off on introducing heavy rainfall into the forecast at this time. Unsettled conditions could into early next week as trade rebuild. The GFS and ECMWF show the upper low slowly filling and drifting westward, raising the possibility that unsettled conditions could continue. && .AVIATION... Kauai continues to be the winner in terms of clouds and showers today thanks to increased low level moisture in the vicinity. Elsewhere, sea breezes have taken over across the island chain this afternoon with interior cloud build ups becoming more evident on visible satellite. These have not produced much in the way of shower activity, but some isolated showers will remain possible before land breezes clear things out overnight. Brief periods of MVFR conditions are possible with heavier showers that do develop, but VFR is expected overall. There are no AIRMETs in effect. && .MARINE... Light easterly winds will prevail through Wednesday as a weak area of high pressure passes eastward just north of the area. Light southerly flow will gradually develop later in the week as a front approaches from the northwest. Winds are expected to swing around to a more northerly direction on Saturday as the front moves over portions of the forecast area. Wind speeds will remain below Small Craft Advisory levels through Saturday. Winds are expected to swing around to the east on Sunday and may become strong enough to reach Small Craft Advisory levels over the typically windy waters around Maui County and the Big Island. The current northwest swell will continue to lower tonight and Wednesday. A larger north northwest swell is expected to arrive on Thursday, peak Thursday night, then lower gradually Friday and Saturday. A High Surf Advisory will likely be issued for this swell for most north and west facing shores. A larger northwest swell is expected to arrive on Saturday, peak Saturday night, then lower gradually Sunday and Monday. Surf heights may reach low end warning levels during the peak of this swell. A series of small southerly swells are expected through the remainder of the week and on through the weekend. Surf will remain small along east facing shores due to the light winds over and upstream of the state. Surf heights will likely rise by early next week as high pressure build in to our north. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Wroe AVIATION...Dye MARINE...Burke Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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