West Side

Today: Breezy. Partly sunny with scattered showers. Highs 72 to 79. Northeast 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 63 to 69. North winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 60 percent.

Wednesday: Mostly sunny with scattered showers in the morning, then partly sunny with isolated showers in the afternoon. Highs 72 to 79. South winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 40 percent.

South Side

Today: Breezy. Partly sunny with scattered showers. Highs around 80. North winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows 61 to 69. North winds 10 to 20 mph becoming northeast up to 10 mph after midnight. Chance of rain 40 percent.

Wednesday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 80. Southwest winds up to 15 mph shifting to the south in the afternoon. Chance of rain 30 percent.

North Shore

Today: Cloudy with frequent showers. Highs 71 to 76 near the shore to around 61 near 5000 feet. North winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 90 percent.

Tonight: Mostly cloudy with scattered showers. Lows 62 to 67 near the shore to 47 to 52 near 5000 feet. Northwest winds up to 15 mph in the evening becoming light. Chance of rain 50 percent.

Wednesday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 72 to 78 near the shore to around 63 near 5000 feet. Light winds becoming south up to 10 mph in the afternoon. Chance of rain 40 percent.

Central Maui

Today: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 77. North winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 60 to 66. North winds 10 to 15 mph shifting to the northwest after midnight. Chance of rain 50 percent.

Wednesday: Mostly sunny with scattered showers in the morning, then partly sunny with isolated showers in the afternoon. Highs around 78. Southwest winds up to 15 mph shifting to the south in the afternoon. Chance of rain 40 percent.

Upcountry

Today: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 53 at the visitor center to around 48 at the summit. North winds up 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 45 at the visitor center to around 41 at the summit. Northwest winds up to 10 mph shifting to the southwest after midnight. Chance of rain 50 percent.

Wednesday: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 55 at the visitor center to around 49 at the summit. South winds up to 20 mph. Chance of rain 40 percent.

East Maui

Today: Cloudy with frequent showers. Highs 71 to 76 near the shore to around 61 near 5000 feet. North winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 90 percent.

Tonight: Mostly cloudy with scattered showers. Lows 62 to 67 near the shore to 47 to 52 near 5000 feet. Northwest winds up to 15 mph in the evening becoming light. Chance of rain 50 percent.

Wednesday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 72 to 78 near the shore to around 63 near 5000 feet. Light winds becoming south up to 10 mph in the afternoon. Chance of rain 40 percent.

Lanai City

Today: Breezy. Mostly sunny with isolated showers. Highs 68 to 74. Northeast winds 15 to 25 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows around 62. Northeast winds 10 to 25 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Wednesday: Breezy. Partly sunny with scattered showers. Highs 68 to 74. Light winds becoming south 10 to 20 mph in the afternoon. Chance of rain 40 percent.

Kaunakakai

Today: Breezy. Partly sunny with scattered showers. Highs 63 to 80. North 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 54 to 68. North winds 10 to 25 mph decreasing to up to 20 mph after midnight. Chance of rain 70 percent.

Wednesday: Breezy. Partly sunny with scattered showers. Highs 63 to 80. North winds up to 15 mph shifting to the south in the afternoon. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A strong high pressure system far northeast of the islands and a trough approaching from the east will support locally strong northeast trade winds over most islands through Tuesday. The trough will pass just north of the islands from late Tuesday through Thursday, bringing a switch to locally strong southeast winds later in the week. Some showers may be briefly heavy the next couple of days, with widespread heavy rain potentially leading to flooding from Thursday into the weekend.

Discussion

Radar shows showers pushing across the islands this evening with the most persistent showers remaining anchored across windward areas and in the vicinity of Big Island and Maui. Radar estimates show that locally heavy rainfall rates, embedded within showers, has increased over the past hour and now nearing 1 to 2 inches per hour. Current lightning data shows a large area of strikes lingering well northeast of Hilo.
For the rest of tonight…showers will continue across windward areas through early Tuesday, as moist and somewhat unstable air lingers over the state. The best chance for locally heavy rainfall and potential thunderstorms, will likely be in the vicinity of Big Island and Maui and the surrounding marine waters, where deeper moisture (satellite based PW imagery) and convergent low level flow continues to stream into the region from the east.
Tuesday through Wednesday…the trade winds will begin to weaken from east to west, as a surface trough to the east sharpens and moves northwestward across the islands through the period. As the trough moves westward, winds will back to the northeast, strengthening over Kauai and Oahu to potentially Wind Advisory levels Tuesday night into Wednesday. A 500 mb low just east/northeast of the islands, will slowly drift back across the state through midweek, before moving to a position southwest of the islands Wednesday night. This pattern will likely shift the band of heaviest showers from the Big Island and Maui briefly Tuesday night and Wednesday, with more persistent widespread showers focused across the western end of the state. The airmass drifting across the region this week will remain moist, with moisture depths well over 11k ft, to sufficiently maintain showers with locally heavy rainfall. Thunderstorm probabilities and stability indices (SW around 0C) suggest the best chances for thunderstorms today will be on Big Island, with better chances for thunderstorms shifting to the west to Kauai and surrounding marine waters Tuesday night through Wednesday night.
Thursday through the weekend…model solutions continue to support a trend toward an extended period of wet and unsettled weather, with a period of potentially significant rainfall spreading across the state Thursday into the weekend. The upper low forecast to slide across the western end of the state Wednesday night, will drift into position over 400 miles southwest of the islands Thursday. Current model solutions depict this upper low rotating slowly east/southeast through the weekend. Forcing associated with the 500mb low, will increase across much of the state Thursday with sufficient forcing lingering through Saturday. Depending on the progression and evolution of this upper low, this pattern could lift deep layered tropical moisture northward across much of the state Thursday through Saturday, with forecast PWs increasing from a statewide average of 1.40″ on Thursday, to over 1.80″ Friday through early Sunday. Model solutions differ to begin the work week, with the placement of the axis of the deepest moisture and potentially heavy rainfall. Thunderstorm probabilities and SW index also support the chance of some thunderstorms during this time. Overall will maintain current forecast trend of showers spreading across the islands through the period, with heavy rainfall possible through Saturday, before showers and heavy rainfall potentially diminish to begin the work week.

Aviation

An upper level low northeast of the Big Island will continue to produce periods of showers and MVFR conditions mainly affecting the eastern islands through early Tuesday morning. These showers may become heavy at times with isolated thunderstorms and brief IFR conditions in +SHRA/TSRA. The western islands will see brief periods of passing showers through Tuesday, mainly over windward and mountain areas in the overnight to early morning hours.
AIRMET Sierra was issued this evening for mountain obscurations over north and east sections of Molokai, Maui and the Big Island. Cloud bands are rapidly filling in from the northeast and will bring more persistent low clouds and showers to the eastern half of the state through Tuesday morning.
AIRMET Tango remains in effect for low level moderate turbulence over and immediately south through west of island mountains. These conditions will decrease over the eastern islands on Tuesday.

Marine

High pressure to our northeast, combined with a trough to the east, will maintain a tight pressure gradient over the coastal and offshore waters. This will keep Small Craft Advisory (SCA) winds and seas over all coastal waters through Tuesday. The trough will move westward over the next several days and will briefly disrupt trade wind flow. As a result, the SCA will likely be extended in time for the northern waters but could be dropped for some areas. However, near-gale force trades are expected to return quickly behind the trough, likely resulting in all waters returning to the SCA by the second half of the week. As the trough moves west, lifts northward, and sharpens, winds in the offshore waters are expected to reach near gale force as early as Tuesday night.
A High Surf Advisory (HSA) remains in effect for east-facing shores through Tuesday afternoon and may need to be extended in some areas due to the strong trades. The current northwest swell will decrease through Tuesday. A second northwest swell will build Wednesday, peak below advisory levels Thursday, and decline Friday. These swell will be helping to boost seas to SCA levels.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Tuesday for Olomana, Kahoolawe, Maui Windward West, Kauai East, Kauai South, East Honolulu, Koolau Windward, Molokai Windward, Molokai Southeast, Windward Haleakala, Kipahulu, South Haleakala, Big Island Southeast, Big Island East, Big Island North.
Small Craft Advisory until 6 PM HST Tuesday for all Hawaiian waters,

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Data Courtesy of NOAA.gov