Photo Credit: James Grenz

Hilo

Today: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 76 to 81 near the shore to 62 to 68 at 4000 feet. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy with scattered showers after midnight. Lows 60 to 67 near the shore to around 54 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Thursday: Partly sunny with scattered showers. Highs 75 to 80 near the shore to 61 to 67 at 4000 feet. North winds up to 15 mph. Chance of rain 50 percent.

Kona

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 82 near the shore to around 66 near 5000 feet. Northwest winds up to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 69 near the shore to 43 to 50 near 5000 feet. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Thursday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 80 to 85 near the shore to around 67 near 5000 feet. Light winds. Chance of rain 40 percent.

Waimea

:

Kohala

Today: Partly sunny in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 76 near the shore to 65 to 72 near 3000 feet. Light winds. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 68 near the shore to 51 to 58 near 3000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Thursday: Partly sunny with scattered showers. Highs around 75 near the shore to 63 to 73 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

South Big Island

:

Puna

Today: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 76 to 81 near the shore to 62 to 68 at 4000 feet. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy with scattered showers after midnight. Lows 60 to 67 near the shore to around 54 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Thursday: Partly sunny with scattered showers. Highs 75 to 80 near the shore to 61 to 67 at 4000 feet. North winds up to 15 mph. Chance of rain 50 percent.

Waikoloa

Today: Mostly sunny with isolated showers. Highs around 81 near the shore to 61 to 68 above 4000 feet. Southeast winds up to 10 mph shifting to the northwest in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers after midnight. Lows 67 to 72 near the shore to 46 to 51 above 4000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Thursday: Sunny and breezy. Highs 79 to 84 near the shore to 62 to 68 above 4000 feet. Northeast winds up to 20 mph.

Detailed Forecast

Synopsis

Weakening trade winds will shift to the north today, with light showers favoring Maui County. A weak front will move down the island chain Thursday and Friday, bringing a modest increase in rainfall over windward and northern slopes and ushering in moderate trade winds into the weekend.

Discussion

The grids have been updated, but no significant changes to the forecast. In the short term, have nudged PoPs and associated fields towards the National Blend of Models (NBM) that have some slightly higher PoP for the windward sides today, and a little higher over the north facing slopes of Kauai and Oahu tomorrow.
The overnight soundings from Lihue and Hilo both showed strong low inversions between 5000 and 5500 feet, and precipitable water (PW) of 0.97 at Lihue and 1.11 at Hilo. The PW values correspond with the satellite derived PW values that show a dry airmass over and upstream of the main Hawaiian Islands.
The low cloud shower band over Maui County has thinned overnight, but there are still just a touch more clouds and showers over the central islands. Trade winds are expected to weaken and becoming more northerly today as a ridge to the north sinks southward towards the islands. As the winds become more northerly, expect showers to shift from focusing more on the north facing slopes mainly of Kauai and Oahu.
A weak front is expected to move down the island chain Thursday and Friday. The front will bring showers to mainly northern and windward slopes of Kauai Thursday morning then move slowly down the island chain through Friday. Mid level ridging is expected to remain over the islands, which will help to limit shower activity. Surface high pressure following the front will bring a brief shot of locally breezy northeasterly trade winds, but winds will quickly drop to moderate strength by Friday as the high moves off to the east. Trades will hold at moderate levels Saturday and may drop off Sunday as another front approaches.

Aviation

Light to moderate northerly winds will prevail today as high pressure to the north weakens. With a relatively dry and stable airmass in place, shower activity will generally be limited. However, a band of low level moisture draped across the islands is contributing to increased cloud cover and light showers across windward areas this morning. This activity will likely continue through today, with the addition of increased clouds across protected leeward areas as sea breezes try to initiate in the lighter flow.
Then winds will strengthen out of the north to northwest heading into this evening in advance of the next cold front, which is expected to approach Kauai late tonight into Thursday morning. This front will bring slightly deeper moisture which will help support more cloud cover and light to moderate showers.
Overall, VFR conditions will prevail with the exception of brief MVFR conditions in passing showers.
No AIRMETs are in effect and none are expected to be needed through the forecast period at this time.

Marine

A progressive pattern in the northern Pacific has set up a series of large to extra- large northwest and north swells to move through the islands.
The first swell (330 deg) will continue to build across the islands through the morning hours. Travel time from offshore buoy NDBC 51101/51001 correlates to the Warning level size surf to peak in the first part of the day on Oahu. Warning level surf will hold for the exposed north and west facing shores of the smaller islands through the day. Seas will respond, reaching the Small Craft Advisory (SCA) threshold for those waters around Kauai, Oahu, windward Maui County, Alenuihaha Channel, and windward Big Island. A short lull between the first and second swell tonight may drop the surf just below Warning levels before the second swell (340 deg) arrives Thursday.
This second swell may be larger which will return warning level surf to the exposed north and west facing shores of the smaller islands by Thursday morning. Taking this into consideration, the current High Surf Warning (HSW) and the SCA has will stay in place through at least Thursday night. It may be extended if the next swell comes in above guidance and holds through Friday.
Next, a mix of north (360-020 deg) and northwest (320 deg) swell energy impacting exposed beaches will likely support advisory- level surf persisting this weekend. For the extended, guidance depicts a near warning-level event arriving next week Tuesday. The northern Pacific looks to remain fairly active and will continue to send swell to the islands for the start of the 2024.
Provided the long duration with large to extra large level surf expected over the next week, significant erosion along exposed north and west facing beaches should be anticipated. This erosion combined with our early morning high tides and warning-level surf could translate to overwash onto our vulnerable coastal roadways and impact properties periodically. The most likely time frames for these impacts will be around early this morning and late Thursday into Friday as the large overlapping events are near their peak.
Surf along east facing shores will remain small through the week due to the light winds locally. East shore beaches exposed to northerly swells will begin to pick up Friday through the upcoming weekend as the swell direction shifts out of the north to north- northeast.
Surf along south facing shores will remain around the winter average through midweek. A slight bump is possible during the second half.
The winds over the local waters will fluctuate from light and variable to moderate north to northeast as the tail-end of passing fronts clip the area. For timing, expect the light winds today, moderate north to northeast winds Thursday, then moderate to locally strong trade winds that set up Friday and Saturday.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 AM HST Friday for Niihau, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
Small Craft Advisory until 6 AM HST Friday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Alenuihaha Channel, Big Island Windward Waters.

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Data Courtesy of NOAA.gov