Hilo

Today: Showers likely, mainly after noon. Mostly cloudy, with a high near 76. Light and variable wind. Chance of precipitation is 60%. New precipitation amounts between a quarter and half of an inch possible.

Tonight: Frequent showers, with thunderstorms also possible after midnight. Some of the storms could produce heavy rainfall. Low around 63. Calm wind. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Saturday: Occasional showers and possibly a thunderstorm. High near 76. Calm wind becoming east northeast 5 to 8 mph in the afternoon. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Kona

Today: Isolated showers, then scattered showers and thunderstorms after noon. Widespread haze after noon. Partly sunny, with a high near 78. West northwest wind around 6 mph. Chance of precipitation is 50%. New rainfall amounts between 1 and 2 inches possible.

Tonight: Scattered showers, mainly before midnight. The rain could be heavy at times. Widespread haze after midnight. Mostly cloudy, with a steady temperature around 69. Northwest wind around 5 mph becoming southeast after midnight. Chance of precipitation is 40%. New precipitation amounts between a tenth and quarter of an inch possible.

Saturday: Scattered showers, mainly after noon. Widespread haze. Partly sunny, with a high near 78. West northwest wind 7 to 9 mph. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch possible.

Waimea

Today: Scattered showers, mainly after noon. Widespread haze after noon. Mostly sunny, with a high near 74. Windy, with a northeast wind 24 to 26 mph, with gusts as high as 38 mph. Chance of precipitation is 30%. New precipitation amounts between 1 and 2 inches possible.

Tonight: Scattered showers. The rain could be heavy at times. Widespread haze after midnight. Mostly cloudy, with a low around 52. Breezy, with an east wind 20 to 22 mph, with gusts as high as 31 mph. Chance of precipitation is 50%. New precipitation amounts between a half and three quarters of an inch possible.

Saturday: Scattered showers. Widespread haze. Partly sunny, with a high near 74. Breezy, with an east wind around 22 mph, with gusts as high as 31 mph. Chance of precipitation is 50%. New precipitation amounts between a half and three quarters of an inch possible.

Kohala

Today: Scattered showers, mainly after noon. Partly sunny, with a high near 70. Very windy, with an east wind 31 to 34 mph, with gusts as high as 65 mph. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Showers likely, then occasional showers and possibly a thunderstorm after midnight. Some of the storms could produce heavy rainfall. Low around 45. Breezy, with an east wind 14 to 18 mph, with gusts as high as 25 mph. Chance of precipitation is 80%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Saturday: Occasional showers and possibly a thunderstorm. High near 70. Breezy, with an east wind around 16 mph, with gusts as high as 22 mph. Chance of precipitation is 80%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

South Big Island

Today: Scattered showers, mainly after noon. Widespread haze. Mostly sunny, with a high near 78. Very windy, with an east wind 29 to 31 mph, with gusts as high as 40 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers. Widespread haze. Mostly cloudy, with a low around 69. Windy, with an east northeast wind 23 to 26 mph, with gusts as high as 34 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Saturday: Scattered showers. Widespread haze. Partly sunny, with a high near 78. Windy, with an east northeast wind around 24 mph, with gusts as high as 31 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Puna

Today: Showers likely. Mostly cloudy, with a high near 74. North northwest wind 6 to 10 mph becoming northeast in the afternoon. Chance of precipitation is 60%. New precipitation amounts between 1 and 2 inches possible.

Tonight: Frequent showers, with thunderstorms also possible after midnight. Some of the storms could produce heavy rainfall. Low around 61. North northeast wind around 8 mph. Chance of precipitation is 100%. New rainfall amounts between three quarters and one inch possible.

Saturday: Occasional showers and possibly a thunderstorm. High near 73. North northeast wind 9 to 11 mph. Chance of precipitation is 90%. New rainfall amounts between a half and three quarters of an inch possible.

Waikoloa

Today: Scattered showers after noon. Widespread haze after noon. Mostly sunny, with a high near 80. Light and variable wind becoming southwest around 6 mph in the afternoon. Chance of precipitation is 30%. New precipitation amounts between three quarters and one inch possible.

Tonight: Scattered showers before midnight. The rain could be heavy at times. Widespread haze after midnight. Partly cloudy, with a low around 61. Breezy, with an east northeast wind around 15 mph, with gusts as high as 21 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Saturday: Scattered showers after noon. Widespread haze. Mostly sunny, with a high near 80. Breezy, with a northeast wind around 16 mph, with gusts as high as 22 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Detailed Forecast

Synopsis

Strong and gusty trade winds will persist across the region into early next week due to a series of strong surface highs to the north and northeast of the islands. Rainfall will remain focused over windward slopes, but an upper level disturbance will give an added boost to these trade showers. The disturbance may even kick off a few thunderstorms Friday and through the weekend over the eastern end of the island chain.

Discussion

The early Friday morning surface map shows a very strong and broad 1047 mb surface high sitting 1600 miles north-northeast of the islands. It is the main source of the strong and gusty easterly trade winds blowing across the main Hawaiian Islands.
A Wind Advisory is in effect for the rest of today for parts of the Big Island and Maui County. An extension of this advisory is possible, through tonight. We will observe the trend before making this decision later today. But the trades will be softening slightly as this high begins moving toward the southeast and weakening some. There were a couple wind alarms overnight, namely Kalaupapa on Molokai and the Kohala Ranch on the lee side of the Kohala Mountains Big Island.
Satellite imagery shows a field of widely dispersed showers mostly upwind of Maui and the windward coast of the Big Island from Upolu Point to the Puna district. Despite the limited cloud cover on satellite, the Koolau Mountains on Oahu have been quite wet in the past couple of hours.
As noted above, the trade winds will be easing off slightly tonight as the high shifts southeastward. A new high, although not as strong, 1043 mb, is forecast to moving into range by Sunday giving the trade winds another boost. The high then drifts south and gradually weaken through the first half of next week. Under this scenario, trade winds are likely to regain very wind status by Saturday night, possibly leading to another Wind Advisory for Maui County and northern Big Island. It won’t be until Wednesday where the trade wind will down to the normal speed of moderate to locally strong.
An upper level low with a pool of cold air of minus 13 to minus 14 degree C at 18k feet will be drifting over the islands from the north in the next 12 to 18 hour, with most of the dynamics situated over the Big Island. This destabilization of the air mass over the islands will enhance the trade wind showers. making some of the showers briefly heavy. Thanks to the breezy trades, these showers will be moving along as passing showers. The winds will also carry the showers well into the lee areas of the smaller islands before dissipating.
The upper low will also be drawing some mid moisture from the south and over the Big Island on Saturday, leading to some frozen precip for the Big Island summits. Further more, there is a slight chance of a thunderstorm, especially on Saturday for the Big Island and east Maui. The upper low over the islands weakens into a trough Saturday night, and warms slightly aloft. Models are pointing to a slightly drier Sunday for the smaller islands, while the Big Island remains showery, along with a slight threat of a thunderstorm. The ECMWF and GFS shows the upper trough moving just south of the Big Island Monday, thus ending the threat of spotty heavy showers and thunderstorms for the Big Island, while a more typical windy trade wind pattern continues elsewhere. As noted above, the trade winds should be back to its normal moderate to locally strong by Wednesday.

Aviation

Strong easterly trade winds will continue today, sustained by an area of impressive high pressure currently located north- northeast of the main Hawaiian Islands. AIRMET Tango remains in effect to account for low level mechanical turbulence for areas over and immediately south through west of mountains. Additionally, since strong winds are forecast to persist throughout the day, AIRMET Tango also accounts for surface winds greater than 30kts in the Alenuihaha Channel and south of the Big Island. Low level wind shear will also continue to be a concern at a few airports.
As an upper level low moves into the area today, an uptick in shower activity is expected, particularly along eastern sections of the islands. MVFR level clouds and reduced visibility in heavier showers will be possible for eastern portions of the Big Island this morning, followed by isolated thunderstorms on leeward slopes of the Big Island this afternoon. Otherwise, VFR conditions will prevail throughout the period.

Marine

A very strong high northeast of the Hawaiian islands and a trough west of the area are creating a tight pressure gradient that is producing strong east winds. A Gale Warning is in effect for the Alenuihaha Channel and the Big Island Leeward Waters through this evening. A Small Craft Advisory (SCA) is in effect for the rest of the Hawaiian Coastal Waters through the weekend. Winds will subside a bit tonight as the high weakens. Winds are likely to strengthen again over the weekend as a new high build north of the area. Winds could reach gale force again Sunday night or Monday.
A long fetch of strong northeast and east trade winds is producing elevated seas. A High Surf Advisory in effect for exposed east facing shores will remain up for the next several days. Surf elsewhere will be below advisory levels. Several long-period northwest swells are expected over the next week. These swells will peak today, tomorrow night into Sunday, and Wednesday into Thursday. The mid-week swell is expected to be the largest of the three. Some trade wind swell will wrap around into north and south facing shores. A small swell from the southern hemisphere will also continue for the next couple of days.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Monday for Kauai Windward, Oahu Koolau, Olomana, Molokai Windward, Maui Windward West, Windward Haleakala, South Big Island, Big Island North and East.
Wind Advisory until 6 PM HST this evening for Molokai, Kahoolawe, Maui Windward West, Maui Leeward West, Maui Central Valley, Windward Haleakala, Leeward Haleakala, South Big Island, Big Island North and East, Kohala, Big Island Interior.
Small Craft Advisory from 6 PM this evening to 6 PM HST Sunday for Big Island Leeward Waters.
Gale Warning until 6 PM HST this evening for Alenuihaha Channel, Big Island Leeward Waters.
Small Craft Advisory until 6 PM HST Sunday 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, Maalaea Bay, Pailolo Channel, Big Island Windward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov