Hilo

Today: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 80 to 86 near the shore to 66 to 74 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Scattered showers in the evening. Lows 64 to 71 near the shore to 54 to 59 at 4000 feet. Light winds. Chance of rain 30 percent.

Saturday: Mostly sunny. Isolated showers in the afternoon. Highs 80 to 86 near the shore to 66 to 74 at 4000 feet. South winds up to 10 mph shifting to the east around 10 mph in the afternoon. Chance of rain 20 percent.

Kona

Today: Partly sunny. Scattered showers in the afternoon. Highs 83 to 89 near the shore to around 69 near 5000 feet. West winds up to 10 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows around 73 near the shore to 48 to 55 near 5000 feet. Light winds. Chance of rain 20 percent.

Saturday: Partly sunny. Scattered showers in the afternoon. Highs 83 to 88 near the shore to around 69 near 5000 feet. North winds up to 10 mph shifting to the west in the afternoon. Chance of rain 40 percent.

Waimea

Today: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 80 near the shore to 69 to 79 near 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then mostly clear with isolated showers after midnight. Lows 64 to 72 near the shore to 55 to 62 near 3000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 40 percent.

Saturday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to 69 to 78 near 3000 feet. Southeast winds up to 10 mph shifting to the north in the afternoon. Chance of rain 50 percent.

Kohala

Today: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 80 near the shore to 69 to 79 near 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then mostly clear with isolated showers after midnight. Lows 64 to 72 near the shore to 55 to 62 near 3000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 40 percent.

Saturday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to 69 to 78 near 3000 feet. Southeast winds up to 10 mph shifting to the north in the afternoon. Chance of rain 50 percent.

South Big Island

Today: Partly sunny. Scattered showers in the afternoon. Highs around 85 near the shore to around 67 near 5000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows around 74 near the shore to around 51 near 5000 feet. East winds around 10 mph. Chance of rain 20 percent.

Saturday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 85 near the shore to around 66 near 5000 feet. East winds 10 to 15 mph shifting to the southeast in the afternoon. Chance of rain 40 percent.

Puna

Today: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 80 to 86 near the shore to 66 to 74 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Scattered showers in the evening. Lows 64 to 71 near the shore to 54 to 59 at 4000 feet. Light winds. Chance of rain 30 percent.

Saturday: Mostly sunny. Isolated showers in the afternoon. Highs 80 to 86 near the shore to 66 to 74 at 4000 feet. South winds up to 10 mph shifting to the east around 10 mph in the afternoon. Chance of rain 20 percent.

Waikoloa

Today: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 86 near the shore to 65 to 73 above 4000 feet. Northwest winds up to 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Lows around 74 near the shore to 50 to 56 above 4000 feet. North winds up to 10 mph shifting to the southeast after midnight.

Saturday: Mostly sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs 83 to 88 near the shore to 65 to 72 above 4000 feet. East winds up to 15 mph shifting to the northwest in the afternoon. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Passing showers will favor Kauai and Oahu today as a trough remains stalled near the Kauai Channel. Moderate to locally breezy trade winds will prevail from Kauai to Oahu's north shore this morning before weakening during the afternoon and evening as the trough weakens further. Elsewhere, light winds will allow for overnight land breezes and daytime sea breezes through the weekend. Light background flow will veer southerly from tonight into next week. An increase in rainfall will be possible over portions of the islands from late Sunday night through Tuesday, though a widespread heavy rainfall event appears unlikely at this time.

Discussion

The front that moved southward into the Kauai Channel yesterday has continued to weaken into a trough overnight and remains stalled in the Kauai Channel early this morning. Latest satellite and radar imagery shows a diffuse band of showers and low clouds associated with this feature moving across Kauai, Oahu, and adjacent waters, though observed rainfall totals since 8pm have been rather light on Oahu and only slightly higher for Kauai. An advanced scatterometer (ASCAT) pass overnight confirmed that moderate to locally breezy northeasterly trade winds are present from Kauai to near the north shore of Oahu. Elsewhere, surface observations reveal much lighter background flow, with near-calm winds from Molokai to the Big Island.
The trough is expected to remain stalled near the Kauai Channel today before eventually dissipating this weekend. Moderate to locally breezy northeasterly trades will remain in place from Kauai to the north shore of Oahu throughout the rest of the morning, but then will weaken from mid-afternoon into tonight. Passing showers will continue to favor Kauai and Oahu throughout the day. Light background flow and drier conditions are expected for the remaining islands, with sea breezes developing from late morning through early evening.
Another front will begin approaching the state from the northwest this weekend. Winds will become lighter and veer southeasterly initially on Saturday, then southerly or southwesterly by Saturday night into Sunday. Regardless, the light flow will support afternoon sea breezes and nighttime land breezes from Friday night into Sunday, especially for the wind-sheltered smaller islands. The general southerly background flow may bring an uptick in showers over some south and southeast facing slopes.
Early next week, a large low pressure system far north of the islands is forecast to move southward closer to the state as a front extending from this feature moves eastward. Models have been fairly consistent for the past few runs that the bulk of significant rainfall and thunderstorm potential will remain north and west of the state, though enhanced moisture from the tropics could be drawn over both the eastern and western ends of the state with a drier slot over the central islands. The forecast has been updated to reflect this thinking and trend closer to the ECMWF and GFS solutions. Model guidance has generally trended drier over the past couple of days, so a widespread heavy rainfall event appears unlikely at this time.

Aviation

A diffuse band of low-level moisture over Kauai and adjacent waters is associated with a stalling and weakening surface boundary that has been bringing clouds and showers to windward Kauai and parts of northern Oahu overnight. MVFR cloud and shower coverage remains sufficiently widespread to warrant AIRMET Sierra for mountain obscuration over windward Kauai. NE trade winds have eased slightly, and AIRMET Tango for low-level turbulence has been cancelled. The boundary is expected to generally weaken in place over the next 12-24 hours, eventually allowing AIRMET Sierra to be cancelled, likely by later today.
Elsewhere across the state, a brief period of light to moderate trade winds is expected in the short term before weakening later today and tonight, delivering just a few windward showers. Winds will likely remain sufficiently light to allow land and sea breezes to prevail in many areas, with mostly dry weather continuing.

Marine

Fresh to locally strong northeast winds will persist over the waters around Kauai and north of Oahu today due to an old frontal boundary that has stalled and weakened into a trough. The latest guidance depicts the trough lingering today, then dissipating over the weekend. Seas at the local buoys and from an earlier satellite altimeter pass are hovering around 10 ft north of Kauai due to a combination of the strong winds and a lingering northerly swell. As a result, the Small Craft Advisory will remain up for the Kauai waters today for winds and seas.
Elsewhere, light to moderate easterly trades will continue today, allowing early morning land breezes and daytime sea breezes to form near the coasts. As the trough in the area dissipates, expect a return of light and variable winds statewide on Saturday. A stronger front will approach the state over the weekend, which will lead to the local winds shifting out of the south to south- southwest and increasing into the moderate to fresh range (strongest western end of the state) Saturday night through Monday as the front nears the islands. Guidance shows this front stalling and weakening near/over the western end of the state through the first half of next week.
Surf along exposed north facing shores will steadily lower into the weekend as a north swell eases. Observations at the offshore buoys, however, did come up slightly overnight due to a slight reinforcement, which supports solid surf holding this morning before easing later today through the weekend. Another north-northwest swell is forecast to arrive and build Sunday night into Monday, then linger through a good portion of next week. This long-lived event will be in response to a gale low dipping southeastward from the Aleutians over the weekend, then stalling around 1000 NM north-northwest of the area Sunday into Monday. Although surf heights should hold below the advisory levels for exposed north and west facing shores through this event, if the swell comes in a few feet higher than predicted, a short-fused advisory will be possible early next week.
Surf along south facing shores will remain above average today, then lower over the weekend as a long-period, south-southwest swell moves through. Surf will rise again early next week as overlapping long-period, south-southwest swells arrive. The first swell will slowly fill in Monday through Tuesday, which has begun to register on the PacIOOS Samoa buoy overnight. Expect a second and larger swell Wednesday through the second half of next week.
Surf along east facing shores will remain up for Kauai and Oahu today as a moderate, short-period northeast swell and the aforementioned fresh to strong northeast winds continue. This will be a short-lived event with a quick drop off expected Saturday.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel.

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Data Courtesy of NOAA.gov