Hilo

Today: Partly sunny with scattered showers. Highs around 81 near the shore to 66 to 71 at 4000 feet. East winds around 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 61 to 69 near the shore to 52 to 57 at 4000 feet. Northeast winds up to 10 mph shifting to the north around 10 mph after midnight. Chance of rain 50 percent.

Tuesday: Mostly cloudy. Scattered showers in the morning, then showers likely in the afternoon. Highs around 80 near the shore to 64 to 70 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Kona

Today: Mostly sunny with isolated showers. Highs around 83 near the shore to around 69 near 5000 feet. Light winds becoming west around 10 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 67 to 72 near the shore to 46 to 54 near 5000 feet. Light winds. Chance of rain 20 percent.

Tuesday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 83 near the shore to around 68 near 5000 feet. Light winds becoming northwest around 10 mph in the afternoon. Chance of rain 40 percent.

Waimea

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to 70 to 76 near 3000 feet. Light winds becoming east around 10 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 62 near the shore to 51 to 60 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny. Breezy. Scattered showers in the morning, then showers likely in the afternoon. Highs around 79 near the shore to 69 to 76 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Kohala

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to 70 to 76 near 3000 feet. Light winds becoming east around 10 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 62 near the shore to 51 to 60 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny. Breezy. Scattered showers in the morning, then showers likely in the afternoon. Highs around 79 near the shore to 69 to 76 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

South Big Island

Today: Mostly sunny. Isolated showers in the afternoon. Highs around 82 near the shore to around 68 near 5000 feet. East winds around 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows around 70 near the shore to around 50 near 5000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Breezy. Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 82 near the shore to around 68 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Puna

Today: Partly sunny with scattered showers. Highs around 81 near the shore to 66 to 71 at 4000 feet. East winds around 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 61 to 69 near the shore to 52 to 57 at 4000 feet. Northeast winds up to 10 mph shifting to the north around 10 mph after midnight. Chance of rain 50 percent.

Tuesday: Mostly cloudy. Scattered showers in the morning, then showers likely in the afternoon. Highs around 80 near the shore to 64 to 70 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Waikoloa

Today: Mostly sunny. Highs around 84 near the shore to 66 to 72 above 4000 feet. Light winds becoming northwest around 10 mph in the afternoon.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 65 to 72 near the shore to 46 to 53 above 4000 feet. East winds around 10 mph. Chance of rain 20 percent.

Tuesday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 84 near the shore to 65 to 71 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A front approaching from the northwest will stall and weaken near Kauai on Tuesday. The front will bring increased shower activity to the state, with Kauai expecting to receive the bulk of the showers. Breezy to locally windy trade winds will fill back in on Tuesday as a new high builds in to our north. Moisture associated with the remnant frontal boundary will allow a wet trade wind pattern through Friday, especially over the west end of the island chain.

Discussion

Have made a few more changes to the forecast through tonight to further boost PoPs. Overnight saw a bit more activity on the radar than originally anticipated. The highest rainfall totals were found at gages over southeast Oahu.
Winds remain on the lighter side as expected ahead of the frontal boundary making its way towards the islands. The boundary is expected to reach Kauai later today as it weakens. A new high pressure system building behind the front will quickly usher in some stronger north winds behind the front. That being said, some sheltered areas will likely still see some afternoon sea breezes today. Even out ahead of the front, expecting to see an uptick in shower activity as we have seen overnight.
Satellite and lightning networks have shown thunderstorms up to the far north-northeast of the islands along the front. Additional thunderstorms are possible along the front, but the main dynamics are expected to remain to the northeast of the islands. An associated upper level trough will bring some instability to the western end of the state, but confidence is low at this time so thunderstorms are not mentioned in the forecast with the front.
In general no changes to the synoptic feature set up. The front will be near Kauai Tuesday, with strengthening northeast trade winds spreading across the area from west to east. The general consensus is that the front will hang up near Kauai and weaken, however some of the models suggest it could move a little closer to Oahu. Regardless, it looks like Oahu and even portions of Maui County will see an uptick in shower activity this week, particularly on the windward sides of the islands. As the trades increase, some of those showers could reach leeward areas.
The breezy to locally windy northeast trade winds will persist into the weekend while what remains of the frontal boundary remains over or near the west end of the state. Thus Kauai and Oahu will likely experience a wet trade wind pattern with a bit less rain expected from Maui County eastward depending on where the moisture axis sets. Guidance does indicate that the moisture axis may shift a bit to the south later in the week, potentially increasing rainfall chances over windward areas of Maui and the Big Island.

Aviation

Satellite continues to show an area of low/mid level moisture moving around, and in the vicinity of the islands this morning. Satellite trends show this area of clouds slowly breaking up, but will likely remain anchored in the region into this afternoon. Surface observations are showing mainly VFR bkn/ovc cigs this morning, with only limited MVFR cigs remaining around the central and eastern islands. Radar trends show showers continuing this morning, with the most persistent showers remaining in channeling flow between islands. An overall light wind field will continue through this afternoon, before winds begin increasing from west to east across the state tonight and Tuesday, as a weakening frontal boundary approaches Kauai from the northwest.
AIRMET Tango continues for potential tempo mod upper lvl turb across the eastern portions of the state, as weak upper dynamics pass south of the region. These conditions will likely diminish this afternoon. Brief periods of MVFR cigs and vsby could generate tempo mountain obscuration across mainly central portions of the state this morning, however, conditions will continue to improve into the afternoon.

Marine

Winds will remain light through this morning as a front moves towards the islands from the northwest. A shallow surface trough that developed near Maui has resulted in light and variable winds from Molokai to Kauai. As the front advances today, winds west of the weakening trough will become northerly and eventually build to moderate strength around Kauai in the afternoon. The front will stall near Kauai Tuesday and gradually dissipate through Thursday or Friday as strong high pressure builds northwest of the state. Trade winds will ramp up to fresh to strong levels late Tuesday, especially along and just north of the front, and persist through at least Thursday. A Small Craft Advisory (SCA) could be needed for most waters, and thunderstorms could develop along the front, most likely across offshore waters.
Forerunners of the next northwest swell have arrived at the offshore buoys northwest of Kauai. This swell is expected to build today and peak Tuesday, when the direction will shift out of the north-northwest. North shore surf may top High Surf Advisory (HSA) levels tonight and Tuesday, followed by a gradual decline Wednesday into next weekend. Background south shore surf will be interrupted by a small south-southwest swell midweek.
East shore surf will remain well below the seasonal average through today. Wind swell will ramp up as the trade winds increase Tuesday and Wednesday, but the islands will lie near the eastern edge of the fetch of strong trade winds, which will limit the growth of the local seas. The latest guidance has backed off slightly, but shows the rough trade wind swell could push east shore surf on Kauai near the HSA level. Seas are projected to build to around seasonal average elsewhere. This trade wind swell will persist through at least Thursday, and the combined seas from the trade wind swell and the northwest to north-northwest swell will likely require an SCA Tuesday through Thursday.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov