Hilo

Tonight: Occasional showers. Lows 59 to 67 near the shore to 46 to 54 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain near 100 percent.

Monday: Occasional showers. Highs 73 to 78 near the shore to around 60 at 4000 feet. East winds 10 to 15 mph. Chance of rain near 100 percent.

Monday Night: Occasional showers. Lows 58 to 66 near the shore to 45 to 53 at 4000 feet. Northeast winds around 10 mph. Chance of rain near 100 percent.

Kona

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows around 69 near the shore to 42 to 48 near 5000 feet. Light winds. Chance of rain 50 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 80 to 85 near the shore to around 64 near 5000 feet. East winds up to 10 mph shifting to the west in the afternoon. Chance of rain 50 percent.

Monday Night: Partly cloudy. Isolated showers in the evening. Lows around 69 near the shore to 42 to 49 near 5000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Waimea

Tonight: Breezy. Scattered showers in the evening, then occasional showers after midnight. Lows 58 to 68 near the shore to 50 to 58 near 3000 feet. East winds 10 to 25 mph. Chance of rain near 100 percent.

Monday: Breezy. Occasional showers in the morning, then showers likely in the afternoon. Highs around 74 near the shore to 64 to 73 near 3000 feet. East winds 10 to 25 mph. Chance of rain near 100 percent.

Monday Night: Mostly cloudy. Breezy. Showers likely in the evening, then scattered showers after midnight. Lows 58 to 67 near the shore to 49 to 57 near 3000 feet. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 70 percent.

Kohala

Tonight: Breezy. Scattered showers in the evening, then occasional showers after midnight. Lows 58 to 68 near the shore to 50 to 58 near 3000 feet. East winds 10 to 25 mph. Chance of rain near 100 percent.

Monday: Breezy. Occasional showers in the morning, then showers likely in the afternoon. Highs around 74 near the shore to 64 to 73 near 3000 feet. East winds 10 to 25 mph. Chance of rain near 100 percent.

Monday Night: Mostly cloudy. Breezy. Showers likely in the evening, then scattered showers after midnight. Lows 58 to 67 near the shore to 49 to 57 near 3000 feet. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 70 percent.

South Big Island

Tonight: Partly cloudy. Breezy. Lows around 71 near the shore to around 47 near 5000 feet. East winds 10 to 25 mph.

Monday: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs around 82 near the shore to around 65 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Monday Night: Mostly clear. Breezy. Lows around 70 near the shore to around 48 near 5000 feet. East winds 10 to 20 mph.

Puna

Tonight: Occasional showers. Lows 59 to 67 near the shore to 46 to 54 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain near 100 percent.

Monday: Occasional showers. Highs 73 to 78 near the shore to around 60 at 4000 feet. East winds 10 to 15 mph. Chance of rain near 100 percent.

Monday Night: Occasional showers. Lows 58 to 66 near the shore to 45 to 53 at 4000 feet. Northeast winds around 10 mph. Chance of rain near 100 percent.

Waikoloa

Tonight: Partly cloudy. Breezy. Lows around 69 near the shore to 45 to 51 above 4000 feet. East winds up to 20 mph increasing to 10 to 20 mph after midnight. Gusts up to 45 mph.

Monday: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs 78 to 86 near the shore to 62 to 67 above 4000 feet. Northeast winds 10 to 20 mph with gusts to 45 mph. Chance of rain 20 percent.

Monday Night: Mostly clear. Breezy. Lows 67 to 72 near the shore to 45 to 51 above 4000 feet. East winds 10 to 20 mph.

Detailed Forecast

Synopsis

Showery remnants of a dissipating cold front will slowly spread across the chain tonight, Monday, and Monday night before moving away by Tuesday. Most of the showers will favor Oahu tonight into Monday, and Maui county Monday into Monday night. Other areas will have cloudy periods and some showers as well, but drier air and more sunshine are expected to return for most areas by Tuesday. A persistent surface high north of the islands will maintain locally windy trades through the middle of the week. Winds will ease a little during the latter portion of the week as the high weakens and moves farther away.

Discussion

A 1033 mb surface high about 850 miles NNE of Kauai is keeping breezy to locally windy trades blowing around the state. A long ribbon of showery low clouds snakes roughly eastward from Kauai to out beyond 140W, connecting up with a cold front. The band is expected to continue to become more diffuse as the trade winds very gradually break it up. This band has not made much southward progress today, and in fact a little northward bump in the ribbon has kept Oahu from being more showery today. The afternoon soundings show a relatively weak inversion near 9-10 kft, and about 1.4 inch total precipitable water (TPW) over Lihue along the dissipating front.
The latest high resolution guidance suggests the upstream portion of the band will adjust its orientation somewhat to be aligned more parallel to the island chain late tonight into Monday. This results in a slightly delayed arrival time for the showers from earlier thinking. Showers are still expected to increase on Oahu overnight tonight and persist into Monday. On Monday, the trades will pull showers in from the convergence band into Maui county as well. As the band becomes more diffuse, overall some additional showers are expected to spread out to Kauai and windward Big Island as well by Monday night, if not sooner. By Tue, most of the moisture from the showery band should be past the islands for much fewer and lighter trade wind showers. The exception will be windward Big Island which should continue to be a bit more showery than usual.
Some of the high resolution guidance, such as the HRRR-HI and NAMnest continues to show the potential for advisory level gusts later Monday or Monday night mainly for leeward Kohala on the Big Island. However, one source of uncertainty is that this should be when increasing moisture is coming into the area with a relatively high and weak inversion. Generally, the shallower lapse rates and higher than normal inversion are not typically particularly favorable for strong downslope winds. There could be some stronger gusts associated with any showers that blow over the mountains there, but as of now confidence is still not high enough to justify putting up a Wind Advisory. Something to keep an eye on, however, as we get closer.
Once we clear out the frontal remnants, looks like a fairly windy and relatively dry week as a new surface high over the North Pacific merges with the current high and sets up shop well to our NNE. The winds will start to ease late in the week as the high weakens and stretches out into a subtropical ridge by next weekend. Moisture will be limited with TPW values oscillating around 1″ and moist-layer depth around 7000 feet. Thus, mostly light and spotty showers are expected for much of the week favoring windward and mauka areas during the nights and mornings. Otherwise fairly nice, albeit gusty trade wind weather for much of the week. Easterly winds may start to get a little more ESE and lighter by next weekend as a trough aloft develops well NW of the islands.

Aviation

Breezy to locally strong trade winds will persist over the next several days. Remnant moisture from a dissipated frontal boundary will shift southward over the islands today. MVFR ceilings and visibilities are likely in showers, but VFR conditions will prevail most areas. Shower activity is expected to increase overnight across the eastern end of the state.
AIRMET Sierra for mountain obscuration is currently in effect for north and east facing slopes of Kauai, and may need to be expanded to include northeast facing slopes of the Big Island or Maui late tonight or tomorrow morning.
AIRMET TANGO remains in effect for moderate low-level turbulence over and downwind of island terrain. This AIRMET is expected to continue over the next several days.

Marine

Persistent strong high pressure centered far north of Hawaii will maintain a very tight pressure gradient between itself and lower equatorial pressure, resulting in an extended period of fresh to locally strong trade winds. As the airmass dries out behind a remnant boundary over the next couple of days, the inversion will lower, resulting in stronger and gusty winds with gale-force speeds possible over the typically windier waters and channels surrounding Maui County and Big Island later Monday through Thursday. The Small Craft Advisory for all Hawaiian waters will remain in effect for the next several days for the strong winds and resulting rough seas.
The current north-northwest swell will progressively decline through the next couple of days. A slightly smaller, medium-period north-northwest (330 degree) swell will arrive around mid-week, with a reinforcing longer- period swell on its heels to close out the week.
Rough surf will continue along east facing shores through the coming week in response to the persistent strong trade fetch over and upstream of the islands. East shore surf could become more elevated and rough around the middle of the week as trades strengthen further.
Surf along south-facing shores will remain small, aside from the possibility of some wrap from the easterly wind waves making it into the more eastern-facing southern exposures.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Tuesday for all Hawaiian waters,

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Data Courtesy of NOAA.gov