Hilo

Today: Mostly sunny with scattered showers in the morning, then mostly cloudy with showers likely in the afternoon. Highs 76 to 81 near the shore to 63 to 68 at 4000 feet. North winds around 10 mph shifting to the northeast in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy. Showers likely in the evening, then occasional showers after midnight. Lows 61 to 68 near the shore to around 54 at 4000 feet. Northwest winds around 10 mph. Chance of rain 90 percent.

Wednesday: Partly sunny. Showers likely in the morning, then scattered showers in the afternoon. Highs 75 to 80 near the shore to around 64 at 4000 feet. Northwest winds around 10 mph shifting to the east in the afternoon. Chance of rain 70 percent.

Kona

Today: Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs around 83 near the shore to around 66 near 5000 feet. Light winds. Chance of rain 30 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 67 to 72 near the shore to 45 to 53 near 5000 feet. Light winds. Chance of rain 20 percent.

Wednesday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 82 near the shore to around 65 near 5000 feet. Light winds becoming west around 10 mph in the afternoon. Chance of rain 50 percent.

Waimea

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs 64 to 82. East winds 10 to 25 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Showers likely in the evening, then occasional showers after midnight. Lows 60 to 66 near the shore to 52 to 60 near 3000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

Wednesday: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs 62 to 80. East winds 10 to 20 mph. Chance of rain 50 percent.

Kohala

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs 64 to 82. East winds 10 to 25 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Showers likely in the evening, then occasional showers after midnight. Lows 60 to 66 near the shore to 52 to 60 near 3000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

Wednesday: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs 62 to 80. East winds 10 to 20 mph. Chance of rain 50 percent.

South Big Island

Today: Breezy. Sunny in the morning, then cloudy with isolated showers in the afternoon. Highs around 80 near the shore to around 65 near 5000 feet. East winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows around 70 near the shore to around 50 near 5000 feet. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Wednesday: Breezy. Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 80 near the shore to around 64 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Puna

Today: Mostly sunny with scattered showers in the morning, then mostly cloudy with showers likely in the afternoon. Highs 76 to 81 near the shore to 63 to 68 at 4000 feet. North winds around 10 mph shifting to the northeast in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy. Showers likely in the evening, then occasional showers after midnight. Lows 61 to 68 near the shore to around 54 at 4000 feet. Northwest winds around 10 mph. Chance of rain 90 percent.

Wednesday: Partly sunny. Showers likely in the morning, then scattered showers in the afternoon. Highs 75 to 80 near the shore to around 64 at 4000 feet. Northwest winds around 10 mph shifting to the east in the afternoon. Chance of rain 70 percent.

Waikoloa

Today: Breezy. Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 80 to 85 near the shore to 64 to 70 above 4000 feet. Southeast winds 10 to 15 mph shifting to the north 10 to 25 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 68 to 73 near the shore to 46 to 54 above 4000 feet. Southeast winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Mostly sunny. Isolated showers in the afternoon. Highs 80 to 85 near the shore to around 65 above 4000 feet. Southeast winds 10 to 15 mph shifting to the north in the afternoon. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Today’s gusty trade winds will gradually ease Wednesday and Thursday, then turn to the southeast and diminish further Friday and Saturday. Stronger east to southeast winds are possible Sunday into next week. A cloud and shower band will linger over the area through Wednesday, bringing passing showers to most windward communities, with some showers spreading leeward. After a somewhat drier period Thursday into Saturday, moisture may increase again over the weekend, with the potential for heavy rain Sunday into next week.

Discussion

A seasonably dynamic weather pattern is anticipated through the forecast period, with showery and breezy trades through Wednesday. Even wetter and windier weather is possible late in the weekend and early next week, but not before a period lighter winds and fewer showers from Thursday into Saturday.
High pressure centered NE of the islands is supporting breezy trade winds, and is pushing moisture associated with a dissipating front over the islands from the E. The dissipating front is marked by a nearly E-W oriented 100-mile-wide band of broken to overcast showery low clouds that extends for at least 500 hundred miles upstream of the islands. Water vapor imagery shows a NE-SW oriented trough just NE of the islands, helping to provide some modest instability. As a result, most cloud tops within the cloud band extend as high as 15 thousand feet, with isolated tops extending as high as 30 thousand feet. Radar shows fast-moving heavy showers over windward slopes that are spreading well leeward on most islands, i.e., Kalaeloa on SW Oahu has received rainfall overnight.
With the frontal moisture axis becoming increasingly E-W oriented upstream of the islands, guidance indicates it will remain over most of the area through at least Wednesday (and maybe even into Thursday), but may not reach the Big Island until tonight. Having said that, it appears that the moisture is sliding S of Kauai in the short term, and will focus over Oahu and Maui County today. However, any northward buckle in the band will bring increased showers right back into Kauai, and this is anticipated by tonight. Some briefly heavy windward showers can be expected through Wednesday as the weak upper trough lingers over the area. When the moisture does finally make it to the Big Island, it looks as though it will extend to the elevation of the Summits, with freezing rain a distinct possibility at times. The trough is expected to weaken Thursday into Friday as an even stronger trough digs in far NW of the islands, leading to some stabilization of the atmosphere.
The new and strong trough will likely spawn a cutoff kona low to the W and NW of the islands over the weekend. Model guidance is still significantly divergent with the location and evolution of this feature, and forecast confidence is reduced from Sunday onward. Although the ECMWF has trended closer to the islands with this kona low over the past couple of cycles, it keeps most of the associated impacts away from the islands. The GFS on the other hand has the low sufficiently close to bring significant impacts, in the form of heavy rain and strong SE winds, starting as soon as Sunday. Residents and visitors should be mindful for the potential for unsettled weather this weekend, and monitor subsequent forecasts for inevitable changes.
After today, trade winds will gradually diminish and veer to the SE through the end of the week as the high to the NE moves steadily E, while the trailing ridge N of the islands weakens in response to an approaching front. Winds may become sufficiently light and SE’ly Thursday through Saturday to allow land and sea breezes to develop. The kona low will develop along the front stalling to the NW, with high pressure strengthening far N and NE of the islands. There is modest agreement amongst the guidance that the tightening low-level gradient will lead to strong E to SE winds Sunday that may last for a couple days, and this has been introduced to the forecast.

Aviation

A strong high pressure system north of the Hawaiian Islands will produce breezy trade winds and push a weakening front into the state today. Expect enhanced cloud and shower activity as the unstable clouds associated with this front hang up over the island chain into Wednesday. Periods of MVFR conditions and showers will favor mountain areas and along north through east facing slopes of all islands with this system. Rainfall potential will trend higher during the overnight to early morning hours for all areas.
AIRMET Sierra remains in effect for Tempo Mountain Obscuration above 020 for N thru E slopes of all islands.
AIRMET TANGO remains in effect below 7000 feet over and immediately south through west of all island mountains due to low level, mechanical turbulence produced by the breezy trade winds.

Marine

This morning’s moderate to locally strong trade winds are associated with the tight pressure gradient between a large northern near 1030 mb high centered just west of 150W and lower equatorial pressure. This high is weakening as it tracks east southeast but will still maintain a tight northeast-to-southwest pressure gradient across our local waters the next couple of days. A cold front approaching the islands from the north and west later this week will weaken the gradient with the front potentially reaching our far northern offshore waters next weekend. The all-water Small Craft Advisory (SCA) continues through this afternoon due to a combination of these breezy trades and resultant elevated seas. As a moderate size north northeast swell moves through the windward waters, significant sea heights will likely achieve 10 foot SCA thresholds. There will be an areal increase of morning showers as the remnants of an old front travel across the local waters.
North facing shore surf is experiencing an upward trend with the arrival of this morning’s moderate size, medium period north northeast swell. While most of the energy associated with this swell was aimed well east of the islands, enough of this energy will angularly spread into the area from the north and east and boost north and east facing shore surf through Wednesday. The more easterly source of this swell will likely result in larger surf lingering longer over more eastern islands. North shore surf heights may flirt with High Surf Advisory (HSA) levels tonight and Wednesday morning. A couple of long period northwest swells, in association with gale force lows passing across the northwestern Pacific through Tuesday, are scheduled to arrive later this week. A small, long period northwest swell will move through the area Wednesday and Thursday with a slightly larger long period northwest swell expected Friday through Sunday. East facing shore chop will remain rough through Wednesday in response to local and upstream moderate to fresh trade flow. Near HSA level east facing shore surf is a possibility through early Wednesday as, along with higher east wind waves, a northeast swell may wrap in.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST this evening for all Hawaiian waters.

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Data Courtesy of NOAA.gov