Hilo

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs around 83 near the shore to 68 to 73 at 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then occasional showers after midnight. Lows around 69 near the shore to around 55 at 4000 feet. East winds 10 to 15 mph shifting to the west after midnight. Chance of rain 80 percent.

Monday: Cloudy with occasional showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 84 near the shore to 68 to 73 at 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 80 percent.

Kona

Today: Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 81 to 86 near the shore to around 68 near 5000 feet. West winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 70 to 75 near the shore to around 56 near 5000 feet. Light winds. Chance of rain 40 percent.

Monday: Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 81 to 86 near the shore to around 68 near 5000 feet. Light winds becoming west around 10 mph in the afternoon. Chance of rain 50 percent.

Waimea

Today: Breezy. Mostly sunny with isolated showers. Highs around 81 near the shore to 68 to 78 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 69 near the shore to 57 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Monday: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 82 near the shore to 68 to 79 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Kohala

Today: Breezy. Mostly sunny with isolated showers. Highs around 81 near the shore to 68 to 78 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 69 near the shore to 57 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Monday: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 82 near the shore to 68 to 79 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

South Big Island

Today: Breezy. Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 85 near the shore to around 72 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows around 71 near the shore to around 54 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Monday: Breezy. Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 85 near the shore to around 72 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Puna

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs around 83 near the shore to 68 to 73 at 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then occasional showers after midnight. Lows around 69 near the shore to around 55 at 4000 feet. East winds 10 to 15 mph shifting to the west after midnight. Chance of rain 80 percent.

Monday: Cloudy with occasional showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 84 near the shore to 68 to 73 at 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 80 percent.

Waikoloa

Today: Mostly sunny. Highs around 85 near the shore to 69 to 75 above 4000 feet. East winds up to 15 mph shifting to the north in the afternoon. Gusts up to 35 mph.

Tonight: Partly cloudy. Lows around 73 near the shore to 52 to 59 above 4000 feet. East winds 10 to 15 mph.

Monday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 85 near the shore to 69 to 75 above 4000 feet. East winds 10 to 15 mph shifting to the north in the afternoon. Chance of rain 20 percent.

Detailed Forecast

Synopsis

High pressure north of the islands will keep moderate to breezy trade winds in place through the middle of the week, with only minor fluctuations in strength from day to day. Rather dry are expected today, with light showers favoring windward and mauka areas. An upper level feature overhead, combined with occasional increases in low-level moisture will bring wetter trade wind weather to the state through the week.

Discussion

Have made some tweaks to the forecast this morning, but no significant changes to the overall forecast philosophy.
A surface high remains far northeast of the islands early this morning, with a ridge to the north. Expect this to maintain a locally breezy trade wind pattern for much of the week. The overnight soundings at Hilo and Lihue continue to show a dry and stable airmass overhead. While the Hilo trade wind inversion remains strong around 7,000 feet, the Lihue trade wind inversion is beginning to weaken. This was expected with an upper level low developing along an upper level trough to the northwest of Kauai.
The GFS and ECMWF both show the low sinking southward over the islands over the next couple of days, but vary in its intensity and exact location. The low will help to erode the trade wind inversion, and that will help to produce more showers across the state. As we head into Monday night, some remnant moisture from an old frontal boundary will approach the islands on the trade wind flow, and when combined with the upper level feature will fuel an increase trade wind showers in both coverage and intensity.
The trades may ease a bit late next week as the high to the northeast weakens slightly, though they will still maintain moderate speeds. Additional surges of increased low-level moisture coinciding with the low aloft lingering nearby have the potential to bring periods of wetter trade wind weather throughout the remainder of next week.

Aviation

Locally strong trade winds will continue, producing moderate low- level turbulence near and downwind of the terrain, requiring AIRMET Tango. VFR conditions will prevail as the the trade winds deliver randomly distributed low clouds and showers that will primarily focus over windward slopes. Brief periods of ISOL MVFR VIS/CIG will be most likely over windward areas during the night and morning, and leeward sections of the Big Island during the afternoon and evening.

Marine

A high pressure system northeast of the Hawaii region will produce moderate to locally strong easterly trades over and upstream of the island chain. A Small Craft Advisory (SCA) remains in effect for the windier waters and channels from Molokai to the Big Island. This SCA will likely be extended through at least Wednesday or Thursday.
An out of season northwest (320-330 degree) swell will gradually decline today. In the extended forecast, Typhoon Guchol will become extratropical in the northwest Pacific during the middle of next week and may send another northwest (300-310 degree) swell into the Hawaii Region by next week Friday or Saturday.
Surf along south facing shores will remain small each day as a mix of long period background south and southwest (170-220 degree) swells move through the region.
Surf along east facing shores will increase slightly through Tuesday with fresh trades winds with decreasing trends from Wednesday onward.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Monday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov