Photo Credit: Tyler Rooke

West Side

Today: Mostly sunny, with a high near 94. Heat index values as high as 101. East northeast wind around 8 mph.

Tonight: Isolated showers before midnight. Partly cloudy, with a low around 76. East northeast wind 7 to 9 mph. Chance of precipitation is 20%.

Monday: Scattered showers, mainly after noon. Mostly cloudy, with a high near 94. Heat index values as high as 101. East northeast wind around 9 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

South Side

Today: Mostly sunny, with a high near 87. East northeast wind 6 to 8 mph.

Tonight: Partly cloudy, with a low around 71. Northeast wind around 9 mph.

Monday: Showers likely after noon. Mostly cloudy, with a high near 86. Northeast wind around 9 mph. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.

North Shore

Today: Isolated showers. Partly sunny, with a high near 86. Breezy, with an east wind 15 to 17 mph, with gusts as high as 24 mph. Chance of precipitation is 20%.

Tonight: Scattered showers. Mostly cloudy, with a low around 72. Breezy, with an east wind 14 to 16 mph, with gusts as high as 22 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Monday: Showers likely, mainly before noon. Mostly cloudy, with a high near 86. Northeast wind around 14 mph, with gusts as high as 18 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Central Maui

Today: Mostly sunny, with a high near 87. East northeast wind 11 to 14 mph, with gusts as high as 18 mph.

Tonight: Scattered showers, mainly after midnight. Mostly cloudy, with a low around 74. East northeast wind 10 to 14 mph, with gusts as high as 18 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Monday: Scattered showers. Mostly cloudy, with a high near 86. Northeast wind around 11 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Upcountry

Today: Mostly sunny, with a high near 76. East northeast wind 7 to 13 mph.

Tonight: Mostly cloudy, with a low around 58. East wind 8 to 11 mph.

Monday: Showers likely after noon. Mostly cloudy, with a high near 75. East northeast wind around 11 mph. Chance of precipitation is 60%. New precipitation amounts between a quarter and half of an inch possible.

East Maui

Today: Showers likely. Mostly cloudy, with a high near 79. East wind 11 to 13 mph. Chance of precipitation is 70%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Frequent showers. Low around 73. East wind 9 to 13 mph. Chance of precipitation is 80%. New precipitation amounts between a quarter and half of an inch possible.

Monday: Frequent showers. High near 79. East northeast wind around 10 mph. Chance of precipitation is 90%. New precipitation amounts between a quarter and half of an inch possible.

Lanai City

Today: Isolated showers after noon. Mostly sunny, with a high near 79. East northeast wind 9 to 11 mph. Chance of precipitation is 20%.

Tonight: Isolated showers before midnight. Partly cloudy, with a low around 67. East northeast wind around 11 mph. Chance of precipitation is 20%.

Monday: Showers likely, mainly after noon. Mostly cloudy, with a high near 79. East northeast wind around 10 mph. Chance of precipitation is 60%. New precipitation amounts between a half and three quarters of an inch possible.

Kaunakakai

Today: Mostly sunny, with a high near 91. Heat index values as high as 99. Breezy, with an east wind 16 to 18 mph, with gusts as high as 25 mph.

Tonight: Partly cloudy, with a low around 75. Breezy, with an east wind 14 to 18 mph, with gusts as high as 25 mph.

Monday: Scattered showers, mainly after noon. Mostly cloudy, with a high near 90. Heat index values as high as 96. Breezy, with an east northeast wind 18 to 20 mph, with gusts as high as 28 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Detailed Forecast

Synopsis

Moderate to breezy trade winds will remain through next week. Showers will continue to ride in on the trades, with an increase in rainfall and humidity likely this afternoon into Tuesday. Brief downpours are expected during this time especially across windward and mountain areas.

Discussion

Persistent high pressure north of the main Hawaiian islands keeps the pressure gradient steep enough to support moderate to breezy trade winds across local waters this morning. Clouds and showers continue to favor windward and mauka areas, representing a weather pattern expected to remain in place through the forecast period. Expect remnant moisture associated with former Tropical Cyclone Guillermo to move through the state today. Heavier showers will affect windward and mountain areas as well as Kona slopes of the Big Island starting this afternoon. Increased moisture will spread to rest of the island chain by Monday. The greatest rainfall, with possible brief downpours, will likely occur over the Big Island and windward Maui from this afternoon through Monday.
By Tuesday afternoon, a drier airmass will begin to move into the eastern half of the state, while moisture continues to linger over the far western end of the state. By Thursday we should see this increased moisture move off to our west as drier trade wind weather returns across the state from the east.

Aviation

Moderate to occasionally breezy east northeasterly trades will act to concentrate most scattered shower activity along the windward coasts and slopes today. Expect periods of MVFR ceilings and visibility, especially for windward Big Island. Isolated showers over leeward sides.
AIRMET TANGO remains in effect for areas below 9000 feet over and immediately south thru west of mountains due to tempo moderate turbulence.
AIRMET SIERRA remains in effect for north thru east sections of Kauai, Oahu, and the Big Island above 2000 feet for mountain obscuration from clouds and showers.

Marine

A surface high pressure system located far northeast of the state will maintain locally strong trade winds through Monday. Also, expect slightly elevated, rough seas over waters exposed to these gusty trade winds. A Small Craft Advisory (SCA) remains in effect for the typically windier waters adjacent to the islands of Maui County and the Big Island through Monday afternoon. This SCA may need to be extended through Monday night for these same waters. The forecast models indicate the surface high far northeast of the area will weaken from Tuesday through Wednesday, which will likely cause a slight decrease in trade winds speeds from Tuesday through Wednesday. Building high pressure to the north and a surface trough passing by well south of the state may result in locally strong trades returning by Thursday.
The trade winds will produce moderate, choppy surf along east facing shores into this evening. The latest model guidance indicates the trade wind swell will likely trend lower from Monday through mid-week due to the weaker trades in the vicinity of the islands, as well as upstream of the state.
The current small south swell will continue to subside through Monday, so expect surf heights to drop below the normal summertime average later today and tonight. Through mid-week, short- to medium-period southeast trade wind swell energy originating from the Southern Hemisphere will keep small surf along exposed shorelines, such as most of the south facing shores of Kauai and the Big Island, as well as select locations along the south shore of Oahu.
Surf will remain nearly flat along most west and north facing shores through mid-week. Small west-northwest swells, which were produced by Northwest Pacific Tropical Cyclone activity, may arrive along some exposed west and north facing shores starting Thursday or Friday. However, confidence about the timing and the size of these swells remains low at this time.

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.

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Data Courtesy of NOAA.gov