Photo Credit: Braden Jarvis

West Kaua’i

Today: Mostly sunny. Isolated showers in the afternoon. Highs around 86 near the shore to around 74 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 69 to 74 near the shore to around 60 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers. Highs around 86 near the shore to around 74 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Isolated showers. Highs around 83. East winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers. Lows 67 to 73. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs around 83. East winds 10 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Breezy. Partly sunny with scattered showers. Highs 73 to 80 in the valleys to around 64 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then occasional showers after midnight. Lows 60 to 65 in the valleys to around 55 above 4000 feet. East winds 10 to 20 mph. Chance of rain 80 percent.

Monday: Mostly cloudy. Breezy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 73 to 80 in the valleys to around 64 above 4000 feet. East winds 10 to 20 mph. Chance of rain 80 percent.

North Kaua’i

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 76 to 85. East winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 63 to 73. East winds 10 to 15 mph. Chance of rain 70 percent.

Monday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 76 to 85. East winds 10 to 15 mph. Chance of rain 70 percent.

East Kaua’i

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 76 to 84. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 61 to 74. East winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Mostly cloudy with scattered showers. Highs 76 to 84. East winds 10 to 15 mph. Chance of rain 50 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.

Data Courtesy of NOAA.gov