Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Breezy. Sunny with isolated showers. Highs 85 to 90 near the shore to around 76 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 71 near the shore to around 62 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs around 86 near the shore to around 75 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

South Kaua’i

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 82 to 89. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 71. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday: Breezy. Partly sunny with scattered showers. Highs 81 to 89. Northeast winds 10 to 25 mph increasing to 20 to 25 mph in the afternoon. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 76 to 83 in the valleys to around 66 above 4000 feet. East winds up to 20 mph becoming 10 to 15 mph in the afternoon. Chance of rain 60 percent.

Tonight: Mostly cloudy with numerous showers. Lows 64 to 69 in the valleys to around 59 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Tuesday: Mostly cloudy. Breezy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 74 to 82 in the valleys to around 65 above 4000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 90 percent.

North Kaua’i

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 87. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 65 to 73. East winds up to 15 mph. Chance of rain 70 percent.

Tuesday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 77 to 87. East winds up to 15 mph. Chance of rain 70 percent.

East Kaua’i

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 75 to 86. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 66 to 75. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tuesday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 73 to 84. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

High pressure far northeast of the islands will keep moderate to breezy trade winds in place through much of the week with only minor fluctuations in strength from day to day. Showers will generally favor windward and mauka areas. Developing troughing aloft coinciding with occasional increases in low-level moisture will bring a trend toward wetter trade wind weather tonight into Tuesday, and again later in the week through the weekend.

Discussion

Satellite and radar imagery show an increase in low clouds and showers across most of the windward waters early this morning, though the showers remain light at this time. A tenth of an inch of rain or less has fallen at a few locations in northern Oahu, windward Kauai, and the Puna district of the Big Island. Surface high pressure remains centered far northeast of Hawaii, with a ridge axis extending westward to the north of the state. This high continues to producing locally breezy easterly trade wind flow across the islands. Water vapor imagery also shows a slight weakness in the upper ridge just west of Kauai and extending southeast along the rest of the leeward waters. According to the 12Z soundings at Lihue and Hilo, this weakness is allowing the trade wind inversion to lift a bit this morning, likely aiding the slight increase in showers.
The area of high pressure northeast of the island chain is expected to strengthen slightly today, yet remain nearly stationary through much of the coming week. This will keep moderate to locally breezy trades over the islands for the next several days with only minor speed fluctuations.
The GFS and ECMWF both continue to show the development of a weak upper-level trough in the vicinity of the state over the next day or two. This trough will meander over and around the islands with varying strength over the next several days. As this occurs, the trade wind inversion will gradually erode. Tonight, low-level moisture from an old frontal boundary east of the state will approach the islands on the trade wind flow. The combination of this additional moisture and the trough aloft is expected to bring an increase in both trade shower coverage and intensity tonight into Tuesday. Both global models indicate the trough deepening into a closed upper low around Wednesday night and lingering directly over the islands through the weekend. Additional surges of increased low-level moisture coinciding with this upper low have the potential to bring periods of wetter trade wind weather at times into early next week, particularly during the overnight through early morning periods.

Aviation

A surface high pressure cell centered far northeast of the state will continue to bring moderate to breezy east or east-northeast trade winds to the islands through the forecast period. This pattern will allow for scattered showers to affect mainly areas along the windward coasts and slopes. Brief periods of MVFR ceilings and visibility accompany any of the more robust activity.
AIRMET TANGO remains in effect below 7000 feet over and immediately southwest through northwest of mountains due to moderate turbulence.

Marine

High pressure far northeast of the state will produce moderate to locally strong easterly trades through most of the week. The Small Craft Advisory remains in effect for the windier waters and channels from Molokai to the Big Island through Wednesday.
Tiny northwest (320-330 degree) swell will continue to linger along north and west facing exposures over the next few days. In the extended forecast, Typhoon Guchol will become extratropical in the northwest Pacific over the next few days and will send another out of season northwest (300-320 degree) swell to Hawaii by Friday or Saturday.
Surf along south facing shores will remain small throughout the week with a mix of long period background south and southwest (170-220 degree) swells. Surf along east facing shores should see a slight increase on Tuesday as trades strengthen then decrease towards the end of the week as the trades weaken.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov