Photo Credit: Tyler Rooke

West Side

Today: Mostly sunny. Breezy. Isolated showers in the morning. Highs 75 to 85. East winds 10 to 20 mph becoming up to 25 mph in the afternoon. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows 66 to 72. East winds up to 20 mph. Chance of rain 20 percent.

Saturday: Breezy. Mostly sunny with isolated showers. Highs 76 to 85. East winds up to 15 mph increasing to up to 25 mph in the afternoon. Chance of rain 20 percent.

South Side

Today: Mostly sunny. Breezy. Highs around 86. Northeast winds up to 15 mph shifting to the east in the afternoon.

Tonight: Partly cloudy. Lows 63 to 72. Northeast winds 10 to 15 mph.

Saturday: Mostly sunny in the morning then becoming partly sunny. Breezy. Highs around 86. Northeast winds 10 to 15 mph shifting to the east 10 to 25 mph in the afternoon.

North Shore

Today: Mostly cloudy. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 73 to 82 near the shore to around 62 near 5000 feet. East winds 10 to 25 mph decreasing to up to 25 mph in the afternoon. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with showers likely. Lows around 67 near the shore to 46 to 52 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Saturday: Breezy. Partly sunny with showers likely. Highs 74 to 82 near the shore to around 63 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Central Maui

Today: Mostly sunny. Breezy. Highs 80 to 86. East winds 10 to 25 mph.

Tonight: Breezy. Partly cloudy with isolated showers. Lows 63 to 69. East winds 10 to 20 mph. Chance of rain 20 percent.

Saturday: Mostly sunny in the morning then becoming partly sunny. Breezy. Isolated showers. Highs 80 to 86. East winds 10 to 20 mph. Chance of rain 20 percent.

Upcountry

Today: Breezy. Mostly sunny with scattered showers in the morning, then partly sunny with showers in the afternoon. Highs around 58 at the visitor center to around 53 at the summit. East winds 10 to 20 mph. Chance of rain 80 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 45 at the visitor center to around 42 at the summit. East winds 10 to 15 mph. Chance of rain 50 percent.

Saturday: Partly sunny. Scattered showers in the morning, then showers likely in the afternoon. Highs around 59 at the visitor center to around 55 at the summit. East winds 10 to 15 mph. Chance of rain 70 percent.

East Maui

Today: Mostly cloudy. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 73 to 82 near the shore to around 62 near 5000 feet. East winds 10 to 25 mph decreasing to up to 25 mph in the afternoon. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with showers likely. Lows around 67 near the shore to 46 to 52 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Saturday: Breezy. Partly sunny with showers likely. Highs 74 to 82 near the shore to around 63 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Lanai City

Today: Sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 73 to 80. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy. Scattered showers early in the evening. Lows around 63. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Saturday: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs 72 to 80. East winds 10 to 20 mph. Chance of rain 20 percent.

Kaunakakai

Today: Mostly sunny. Breezy. Highs 67 to 84. East winds 10 to 25 mph decreasing to up to 20 mph in the afternoon.

Tonight: Breezy. Partly cloudy with isolated showers. Lows 55 to 71. East winds up to 20 mph. Chance of rain 20 percent.

Saturday: Breezy. Mostly sunny with isolated showers. Highs 67 to 84. East winds up to 20 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Locallly strong trades will weaken slightly today, becoming locally breezy by tonight. Showers will tend to focus over windward and mauka zones through the weekend, especially at night, with a low potential for inland showers on Saturday afternoon.

Discussion

Locally strong trades are beginning to weaken and veer to ESEly as high pressure establishes over the northeast Pacific Basin. Winds will further weaken into the locally breezy category overnight with additional slight veering possible into Saturday. Trades will tend to focus showers over windward and mauka zones during this time, particularly overnight and during the early morning. Trades will acquire an increasingly unstable, or at least weakly stable, character during the next 72 hours as an upper jet impinging on the forecast area from the west forces a period of mid-level troughing to develop directly over the islands.
Water vapor imagery indicates cyclonic flow has already begun to take shape over the islands, its effects already manifesting in the form of thunderstorm development directly beneath the upper wave/southwest of the islands, as well as in the modest deepening of trade wind showers affecting windward slopes this morning. A few locally heavy showers are evident on radar and cannot be ruled over windward areas, but strong trades will ensure any heavier showers move quickly. Likewise, diminishing stability and strong trades will allow for effective leeward penetration of showers in favored areas. However, it is already evident that showers over the smaller islands are being steered northwestward, parallel to the island chain, by stout southeasterly flow centered at 850mb. This is producing some degree of shadowing west of Maui, a trend that is likely to continue through the weekend.
As the low deepens overhead Saturday and Sunday, 500mb temperatures falling to a decent-but-not-impressive -10C or so will support 700-500mb lapse rates falling to around -7C/km, mainly over the eastern end of the state. With the addition of daytime heating, interior portions of the Big Island should have no issue generating some afternoon thunderstorms Saturday and Sunday. The primary change to the morning forecast package was therefore to add thunder to the Big Island for both Sat and Sun afternoon. For the smaller islands, expect the next 3 days to be characterized by unstable trades supportive of briefly heavy showers mainly over windward and mauka zones. Shadowing concerns alluded to above only increase during this time as low- level winds also veer to ESE. Absent island interaction/leeward plume development, suspect this period of unstable ESE trades may underachieve for many locations west of the Big Island.
Height rises in the wake of the departing upper trough bring a return to more typical stable, locally breezy trades by early next week.

Aviation

AIRMET Tango for low-level turbulence will remain in place as locally strong and gusty easterly trade winds continue into Saturday. VFR conditions will prevail, but the trade winds will deliver low clouds and showers that will primarily affect windward slopes and coasts with brief periods of MVFR VIS/CIG in SHRA.

Marine

A high pressure system located far north-northeast of the islands will keep fresh to strong east-southeasterly trade winds in the forecast across the region today. A Small Craft Advisory (SCA) was extended in time in effect for most central and eastern coastal waters through early Saturday morning due to strong winds and rough seas. Wind speeds in the windier waters and channels near Maui and the Big Island will remain near gale strength today. Winds will begin to ease this weekend, and SCA conditions will decrease in coverage back to the more typical windier waters and channels surrounding Maui and the Big Island. Combined seas will approach 10 feet over most windward waters today then ease a bit through the weekend.
The current northwest swell will decline today with surf heights rapidly decreasing along north and west facing through through Sunday. Nearly flat surf conditions expected along north and west facing shores by Monday and Tuesday. A period of fresh to strong trades upstream of the islands will keep short period, higher wind waves along many northeastern and eastern facing shores into the weekend.
A small background south swell will continue today, as a slightly larger and longer period south swell will begin to build into the region later this afternoon. This next south swell energy will peak on Saturday. This next south swell will raise surf heights along south facing shores by a couple of feet into the fun size range through Sunday and then decline into early next week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Saturday for Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov