Photo Credit: Tyler Rooke

West Side

Today: Mostly cloudy. Showers likely in the morning, then scattered showers in the afternoon. Highs 75 to 82. Light winds. Chance of rain 60 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 65 to 72. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny. Scattered showers in the afternoon. Highs 77 to 84. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

South Side

Today: Mostly cloudy. Scattered showers in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs around 84. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 65 to 71. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs around 85. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

North Shore

Today: Mostly cloudy. Showers likely in the morning, then showers likely and isolated thunderstorms in the afternoon. Highs 74 to 81 near the shore to around 65 near 5000 feet. Southeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 68 near the shore to 50 to 55 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 75 to 82 near the shore to around 67 near 5000 feet. Southeast winds 10 to 15 mph. Chance of rain 50 percent.

Central Maui

Today: Mostly cloudy. Scattered showers in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs around 83. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 67. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs around 84. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Upcountry

Today: Mostly cloudy. Showers likely in the morning, then showers likely and isolated thunderstorms in the afternoon. Highs around 59 at the visitor center to around 53 at the summit. Light winds. Chance of rain 70 percent.

Tonight: Cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 49 at the visitor center to around 43 at the summit. Light winds becoming northeast around 10 mph after midnight. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers. Highs around 62 at the visitor center to around 55 at the summit. East winds 10 to 15 mph. Chance of rain 50 percent.

East Maui

Today: Mostly cloudy. Showers likely in the morning, then showers likely and isolated thunderstorms in the afternoon. Highs 74 to 81 near the shore to around 65 near 5000 feet. Southeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 68 near the shore to 50 to 55 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 75 to 82 near the shore to around 67 near 5000 feet. Southeast winds 10 to 15 mph. Chance of rain 50 percent.

Lanai City

Today: Mostly cloudy with showers likely. Highs 71 to 77. Light winds becoming north around 10 mph in the afternoon. Chance of rain 60 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 64. Light winds. Chance of rain 20 percent.

Friday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 72 to 78. Light winds becoming east around 10 mph in the afternoon. Chance of rain 50 percent.

Kaunakakai

Today: Mostly cloudy. Showers likely in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 67 to 83. Light winds becoming north around 10 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 56 to 71. Northeast winds around 10 mph. Chance of rain 20 percent.

Friday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 67 to 85. East winds around 10 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

Light winds and humid conditions will prevail through Friday as a trough stalls and gradually weakens near Kauai and Oahu. The trough will bring the potential for thunderstorms and locally heavy showers today, especially to Kauai and Oahu, although all islands may see a thunderstorm this afternoon. A drier and more settled trade wind weather pattern is expected as the weekend begins, with limited showers expected into early next week as trade winds gradually turn to the southeast and diminish Sunday and Monday. Light winds and increased moisture are anticipated again during the middle part of next week.

Discussion

A deep-layer low centered about 650 miles NNW of Kauai has an associated convergence band that is producing scattered thunderstorms along a NE-SW oriented line that intersects leeward Kauai coastal waters this morning. Meanwhile, additional thunderstorm clusters are developing just E of this line primarily affecting Oahu and surrounding waters. Water vapor imagery shows a short wave aloft aloft supporting the strong convection along this band,with convection most vigorous just NE of the coastal waters. Another short wave trough aloft is noted in water vapor imagery – sharpening along 165W – and moving steadily E toward the islands.
Although our typical trade-wind-producing high is still centered to the NE of the islands, the presence of the low and convergence band has turned the low-level flow to the S over Oahu, and to the SE over Maui and the Big Island, with light winds prevailing. As has been the case for several days, broken to locally overcast mid- and high- level clouds blanket island skies.
Ongoing forecast philosophy is supported by latest round of guidance, generally anticipating the deep-layer low to move E and weaken well N of the islands over the next several days. This will lead to a light and variable wind regime, although winds will still favor a southerly direction this morning. As some of the high- resolution model guidance had been indicating, the area of persistent convection W of Kauai steadily diminished through the evening yesterday while convection near Oahu steadily increased in area and intensity. Thunderstorms with prolific lightning moved over Oahu as heavy showers and thunderstorms moved ashore from the S, with a few strong thunderstorms dropping pea- to dime-sized hail. HNL airport got more rain (~1.6″) in an hour overnight than it had during the first 22 days of the month.
With the trough dissipating over Kauai and Oahu, light and variable winds and lingering moisture will ensure somewhat humid conditions to day and Friday, with surface dew points near 70F. While afternoon sea breezes will likely be the best trigger for shower development over land, the surface trough and support aloft will trigger localized heavy shower development this morning, with embedded strong to near-severe thunderstorms.
Light to moderate trade winds are expected for the the weekend as the high to the NE resumes control over island weather, with a stable regime leading to just a few windward showers. By early next week, a regime similar to the current one appears to unfold once again. Low pressure currently to the distant NW will pass N of the islands, leading to a stalling low-level trough that is likely to bring light winds and increased moisture from Tuesday through Thursday.

Aviation

A surface trough along with an upper level trough will continue to support isolated to scattered thunderstorms for mainly kauai and Oahu and their adjacent waters throughout the day today. Light southeast winds with local land/sea breezes will continue today as well. Periods of MVFR conditions embedded in the showers can be expected with isolated IFR conditions in the heavier showers/thunderstorms.
As the surface trough makes its way down the island chain, clouds and showers will drift over the islands from the south. Chances for showers and thunderstorms will initially favor Kauai and Oahu earlier in the day, though sea breezes could trigger some interior convection on all islands by the afternoon. Additionally an upper level shortwave trough also looks to enhance instability later today, increasing the chances for heavy rain and thunderstorm development over all the islands.
Currently an AIRMET Sierra is in place for mountain obscuration over eastern areas of the Big Island as well as the entire island of Oahu due to frequent clouds and showers, this will likely continue through the day and may need to be expanded to other islands. SIGMET UNIFORM also remains in effect over the Hawaiian islands for embedded thunderstorms, this will likely continue through the day.

Marine

A surface low pressure system centered about 550 nm north- northwest of Kauai will move toward the east-northeast at about 10 kt today. A surface trough associated with the low is located just west of Kauai. Clouds and showers with embedded isolated thunderstorms are along and east of this trough, which is moving slowly eastward. This feature is expected to move across the western end of the island chain through this evening, and eventually dissipate by Friday. Elsewhere, a surface high pressure system is centered far northeast of Hilo. These weather features will keep the background winds gentle across the western half of the state, while moderate east to southeast winds will persist over the eastern half of the state today. The winds over the Maui County and Big Island Windward Waters and the Alenuihaha Channel have weakened early this morning. Therefore, the Small Craft Advisory (SCA) is being cancelled for those marine zones. The current forecast indicates the winds will remain below the SCA criteria over all waters through Friday. High pressure building north of the region from Friday night through Saturday are expected to cause the trade winds to strengthen over the eastern end of the state. This may result in the issuance of a SCA for the Alenuihaha Channel and waters south of the Big Island starting Saturday. The forecast guidance remains in relatively good agreement that another surface low pressure may move to a position far northwest of the region from Sunday through Monday. This scenario will likely cause the winds to gradually weaken early next week.
Surf is expected to remain below the High Surf Advisory criteria along all shorelines through this weekend. A fetch of strong easterly winds just upstream of the state will continue to produce moderate, choppy surf along east facing shores today, and then will gradually lower from this evening through Friday. The current short- period north swell (020 degrees) will steadily subside this morning. A mix of small northwest and north-northwest swells (310-330 degrees) will maintain modest surf along most exposed north and west facing shorelines from later today and tonight into this weekend. The current small, medium-period south swell (190 degrees) will slowly fade through Friday, with only small background south swell energy expected this weekend.

HFO Watches/Warnings/Advisories

Flood Watch through this afternoon for Oahu.

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Data Courtesy of NOAA.gov