Photo Credit: Braden Jarvis

West Kaua’i

Today: Partly sunny. Windy. Isolated showers in the morning, then scattered showers in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 85 near the shore to around 72 above 3000 feet. East winds 10 to 30 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Windy. Isolated showers in the evening, then scattered showers after midnight. Lows around 71 near the shore to around 61 above 3000 feet. East winds 15 to 30 mph. Chance of rain 50 percent.

Wednesday: Partly sunny. Windy. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 85 near the shore to around 72 above 3000 feet. East winds 20 to 30 mph with gusts to 50 mph. Chance of rain 50 percent.

South Kaua’i

Today: Mostly cloudy. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 78 to 84. East winds 20 to 25 mph. Chance of rain 40 percent.

Tonight: Windy. Mostly cloudy with scattered showers. Lows around 70. East winds 20 to 30 mph. Chance of rain 50 percent.

Wednesday: Windy. Partly sunny with scattered showers. Highs 77 to 84. East winds 25 to 30 mph with gusts to 50 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly cloudy. Breezy. Scattered showers in the morning, then numerous showers in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 70 to 80 in the valleys to around 62 above 4000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Windy. Numerous showers in the evening, then showers after midnight. Lows 64 to 69 in the valleys to around 58 above 4000 feet. East winds 15 to 30 mph. Chance of rain 90 percent.

Wednesday: Windy. Mostly cloudy with numerous showers. Highs 70 to 79 in the valleys to around 62 above 4000 feet. East winds 20 to 30 mph with gusts to 50 mph. Chance of rain 70 percent.

North Kaua’i

Today: Breezy. Mostly cloudy with scattered showers. Highs 74 to 86. East winds 10 to 25 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 64 to 73. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 70 percent.

Wednesday: Windy. Partly sunny with scattered showers. Highs 73 to 85. East winds 10 to 30 mph increasing to 20 to 30 mph in the afternoon. Chance of rain 50 percent.

East Kaua’i

Today: Breezy. Mostly cloudy with scattered showers. Highs 70 to 81. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 65 to 74. East winds 15 to 25 mph. Chance of rain 70 percent.

Wednesday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 70 to 81. East winds 15 to 25 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A strong high pressure system will build in north of the Hawaiian Islands this week. Easterly trade winds will gradually strengthen over the next few days, with windy trades and stronger gusts forecast to blow from Wednesday into Friday. Upstream moisture riding in on the trade winds will produce periods of showers favoring windward mountain slopes, some of these stronger showers will spread into drier leeward areas. These strong trade winds will slowly ease into moderate to breezy thresholds from Saturday to Sunday as the high center north of the state weakens.

Discussion

The weather picture this morning remains fairly similar to last night with trough, dissipated front, northwest of the state and a building high pressure system farther north of the trough boundary. The long unstable cloud band currently moving through the state will likely drift through all islands later this morning with a brief decrease in shower trends forecast for the afternoon time period. An upper level low continues to develop roughly 900 miles west of Kauai. High cirrus clouds associated with the eastern edge of this upper low will fill in over the island chain today.
Wet trade wind weather will continue through much of the week with higher shower coverage in the overnight to early morning hours. A strong high pressure system will slowly build in far north of the islands over the next few days with a very strong central pressure forecast at around 1050 mb. Trade winds will steadily increase today and tonight, and then peak at windy levels from Wednesday to Thursday. Wind advisories were issued this morning starting later this evening for the windier zones of each island. Maui and Big Island summits wind speeds will be lighter and remain below wind advisory thresholds during this wind event.
The developing upper level cutoff low west of the state will tend to add some instability into the mix over the western islands. The impacts of this low on island weather will depend upon how close the upper level low center and cold pool gets to Kauai and Oahu. For now we are keeping fairly tame wet trade winds in the forecast. However, if this cutoff low moves closer to the Hawaiian Islands, then we could see a brief period of heavy showers and thunderstorms mainly over Kauai, and possibly as far east as Oahu. Stay tuned.
Trade winds will slowly ease over the weekend with breezy conditions, and mostly windward showers, favoring the overnight to early morning hours.

Aviation

Breezy to locally windy easterly trade winds will persist, with clouds and showers favoring windward slopes and coasts. Expect periods with MVFR CIGs/VSBYs in showers, particularly overnight through the early morning hours. Some showers will spill over into leeward areas of the smaller islands periodically.
AIRMET Sierra for mountain obscuration remains in effect for N through E sections for Maui and the Big Island.
AIRMET Tango for moderate low-level turbulence over and southwest through northwest of mountains remains in effect for all islands.

Marine

A 1044 mb surface high far N of the islands will drift E over the next day or two, peaking near 1052 mb as it passes N of the islands tomorrow, leading to increasingly strong E trade winds. The high will drift S as it gradually weakens from Thursday through Saturday. Based on an overnight ASCAT pass, trade winds are already on the increase. A Small Craft Advisory is in effect for all waters, and will be upgraded to a Gale Warning for the windier zones tonight. The Marine Weather Message (MWWHFO) contains the details. Winds will ease slightly Friday and Saturday, but will remain strong to near gale-force.
A nearby fetch of N winds has generated a short-period (~10 seconds) N swell that will gradually build today and peak Wednesday (near 5 feet) before diminishing. Peak surf heights will remain below High Surf Advisory heights. The strengthening trade winds will drive increasing short-period wind waves toward the islands from the E over the next couple of days, with E shore peak surf heights likely exceeding 10 feet (thus requiring a High Surf Advisory) from Wednesday into Friday. Anomalously strong low pressure in the distant SE Pacific has an associated fetch that may deliver a small, medium-period SSE swell by the weekend.

Fire weather

Long-term conditions over leeward areas are drier than normal for this time of year. Though the Keetch-Byram Drought Index measured in Honolulu will remain well below the critical 600 mark this week, the strong and gusty trade winds will elevate the fire danger over the drier leeward areas over the next several days.

HFO Watches/Warnings/Advisories

Wind Advisory from 6 PM this evening to 6 PM HST Thursday windier areas across the state.
Small Craft Advisory until 6 PM HST Thursday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Big Island Windward Waters.
Small Craft Advisory until 6 PM HST this evening for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Gale Warning from 6 PM this evening to 6 PM HST Thursday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov