Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 81 near the shore to around 69 above 3000 feet. East winds 10 to 25 mph with gusts to 50 mph. Chance of rain 50 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows around 67 near the shore to around 56 above 3000 feet. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 20 percent.

Saturday: Breezy. Mostly sunny with isolated showers. Highs around 81 near the shore to around 69 above 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

South Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs around 80. East winds 20 to 25 mph with gusts to 50 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 63 to 68. East winds 15 to 25 mph with gusts to 45 mph. Chance of rain 70 percent.

Saturday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 80. East winds 15 to 20 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Mostly cloudy. Windy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 68 to 76 in the valleys to around 63 above 4000 feet. East winds 20 to 30 mph with gusts to 50 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Windy. Numerous showers in the evening, then showers after midnight. Lows 56 to 61 in the valleys to around 50 above 4000 feet. East winds 15 to 30 mph with gusts to 50 mph. Chance of rain 90 percent.

Saturday: Mostly cloudy. Breezy. Showers in the morning, then scattered showers in the afternoon. Highs 68 to 76 in the valleys to around 63 above 4000 feet. East winds 15 to 25 mph. Chance of rain 90 percent.

North Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 73 to 80. East winds 10 to 25 mph with gusts to 50 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 59 to 68. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 50 percent.

Saturday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 73 to 80. East winds 10 to 20 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 73 to 80. East winds 15 to 25 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 57 to 69. East winds 15 to 25 mph. Chance of rain 70 percent.

Saturday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 73 to 80. East winds 15 to 20 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A strong high pressure system north to northeast of the state will continue to produce blasting trade winds across the Hawaiian Islands into the weekend. Expect a slight decrease in trade wind speeds from Saturday to Sunday as the high center slowly drifts eastward away from the island chain. However, breezy trade winds will continue to blow across the region into the first half of next week. Several upper level lows along an upper trough will remain over the islands keeping periods of beneficial showers in the forecast through much of next week, especially during the overnight and early morning hours.

Discussion

Blasting trade winds with strong potentially damaging wind gusts remain in the forecast into the weekend as a strong high pressure system lingers north to northeast of the state. Wind speeds will slowly decrease into the breezy range from Saturday to Sunday as the high center drifts slowly eastward away from the region. High Wind Warning and Wind Advisory products were extended in time statewide through Saturday morning for the warning and Saturday afternoon for the advisory. High Wind Warning products will likely be dropped to advisory levels by tonight for Oahu and Saturday morning for the Big Island as wind speeds begin to ease.
Regional GOES satellite shows an upper level low on water vapor imagery just south of the island chain. This low is embedded in an upper trough extending from west to east over the islands. High level cirrus clouds outline this unstable upper level trough. Upper level divergent forcing from this system will keep periods of trade wind showers in the forecast through much of next week. This upper trough will likely produce seven days of beneficial rainfall over all islands with the highest shower amounts focused over the windward and mountain slopes as Pacific moisture is lifted over island mountains. Shower coverage will tend to favor the overnight to early morning hours due to typical higher nocturnal rainfall trends in the tropics.
Trade wind speeds decrease slightly from windy trades to more breezy wind speeds from late Saturday into early next week. However, another strong high pressure system builds northwest of the region, crossing the Dateline far north of the state from Tuesday to Wednesday. A couple of challenges are developing with the medium range wind forecast for next week. Initially on Tuesday we may see more moderate to locally breezy trade winds, due to a combination a cold front passing far north of the state weakening the surface ridge and divergence from the upper trough potentially forming a weak surface trough over the islands. This surface trough may weaken pressure gradients over the state and shift the belt of strongest winds slightly north of the island chain.
Global forecast model guidance is coming into better agreement on the strength of this surface trough and the strength of the trade winds by the middle of next week. Our confidence is increasing on keeping locally windy trade winds out of the forecast from Tuesday through Wednesday. Either way longer range model solutions continue to agree that another round of blasting trade winds will return by next Thursday and Friday. Overall this breezy to windy trade wind pattern may remain locked in over the Hawaii region through for much of next week with subtle changes day to day changes in wind speeds, stay tuned.

Aviation

A strong surface high pressure system located far north-northeast of the state continues to produce very strong and gusty trade winds across the islands. Sustained surface winds in excess of 30 kt with higher gusts will continue to be possible for some locations today. Based on the fact that PHOG on Maui had winds of about 40 kt at 2000 ft AGL Thursday afternoon, there will likely be low-level wind shear there again this afternoon. Scattered to broken low clouds with embedded scattered showers continue to stream into the windward sides of most islands, especially the Big Island. Therefore, expect brief periods of MVFR conditions over the windward sections of most of the islands. VFR conditions will likely prevail over most leeward areas.
AIRMET Tango remains in effect for sustained surface winds of 30 kt or greater. AIRMET Tango also remains in effect for moderate to isolated severe low-level turbulence over and downwind of the higher terrain on all islands. Both of these AIRMETs will likely be needed through this afternoon. In addition, AIRMET Sierra remains in effect for mountain obscuration over the windward Big Island.

Marine

Strong easterly trade winds are here to stay through next week, with periods of gales possible in the typically windier areas and channels. Gales are mostly likely in these areas through Saturday, then may near these levels again late next week with a similar pattern potentially setting up. Morning buoy observations reflect the strong winds and continue to climb, with wave heights now in the 10 to 15 ft range (around 6 ft of that in the 2-4 second band).
Surf along east facing shores will remain rough through next week in response to the aforementioned pattern we are locked in. Warning-level surf is likely to persist through Saturday, then back to the advisory level Sunday through early next week. Impacts associated with this long-duration event associated with a combo of strong onshore winds and large surf will translate to significant beach erosion, powerful rip/alongshore currents, and occasional overwash onto vulnerable sections of the coast (best overwash chances at and around the peak daily high tide cycle just before/around daybreak).
Surf along north and west facing shores peaked overnight from a north-northwest swell moving through, but will ease quickly today as it moves out (mostly missed us to the north). A small long-period northwest swell is expected to fill in over the weekend, then peak through the first half of next week.

HFO Watches/Warnings/Advisories

High Wind Warning until 6 AM HST Saturday for Kohala, Big Island North.
High Wind Warning until 6 PM HST this evening for Waianae Coast, Oahu North Shore, Central Oahu, Waianae Mountains, Honolulu Metro, Ewa Plain, Koolau Leeward.
Wind Advisory from 6 PM this evening to 6 AM HST Saturday for Waianae Coast, Oahu North Shore, Central Oahu, Waianae Mountains, Honolulu Metro, Ewa Plain, Koolau Leeward.
Wind Advisory until 6 AM HST Saturday for most of the Hawaiian Islands.
High Surf Warning until 6 PM HST Saturday for all exposed east facing shores.
Gale Warning until 6 PM HST Saturday for Kaiwi Channel, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 PM HST Saturday for most Hawaiian coastal waters.

Data Courtesy of NOAA.gov