Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Mostly sunny. Highs 82 to 87 near the shore to around 72 above 3000 feet. Northeast winds up to 10 mph shifting to the southeast in the afternoon.

Tonight: Partly cloudy. Lows around 69 near the shore to around 58 above 3000 feet. East winds 10 to 15 mph.

Tuesday: Mostly sunny with isolated showers. Highs around 85 near the shore to around 71 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Mostly sunny. Isolated showers in the morning. Highs 77 to 85. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows around 70. Northeast winds around 15 mph. Chance of rain 20 percent.

Tuesday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 76 to 84. Northeast winds around 15 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 72 to 82 in the valleys to around 63 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 63 to 68 in the valleys to around 57 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Breezy. Cloudy with showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 70 to 82 in the valleys to around 62 above 4000 feet. East winds 10 to 20 mph. Chance of rain 80 percent.

North Kaua’i

Today: Mostly sunny with isolated showers. Highs 75 to 84. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 62 to 71. East winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 74 to 85. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly sunny with isolated showers. Highs 72 to 83. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 64 to 74. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 71 to 83. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Fairly dry conditions continue through much of the week as trade winds steadily strengthen into the breezy to strong range by Wednesday and Thursday. Wind speeds will then start a gradual decline into the moderate to locally breezy range from Thursday night into next weekend. An upper level low will develop and pass just south of the Big Island from Wednesday afternoon through Friday. This upper level disturbance may enhance rainfall coverage over the eastern half of the state lasting into next weekend.

Discussion

The satellite and local radar imagery around the Hawaiian Islands this morning continues to show fairly stable clouds with just a few showers popping up over the coastal waters. Upper air radiosonde balloon observations from Lihue earlier this morning at 2 AM HST (12Z) show subsidence temperature inversion heights around the 5,000 foot level. These low inversion heights are caused by the downward vertical motions (subsidence) under the upper level ridge, which warms and dries the atmosphere aloft, creating a stable temperature inversion layer, limiting vertical cloud growth, and decreasing rain shower activity. These more stable conditions will continue through the first half of this week.
The main weather story for the next several days will be a steady strengthening of the trade winds from moderate to breezy levels through the day starting a few hours after sunrise, then increasing into the breezy to windy range by Tuesday, with wind speeds peaking on Wednesday across the island chain. These stronger wind speeds will likely reach wind advisory thresholds for some of our windier zones possibly starting on Tuesday night. The highest summits of Mauna Kea and Mauna Loa where wind speeds are expected to jump up to warning levels later this morning as an upper level jet streak dives down over the island from the north. As such, a High Wind Warning has been issued for both summits today.
In the long range outlook, global weather models continue to show an upper level cut off low moving into the Hawaii region. Current operational runs show the center of this low passing south of the Big Island by Wednesday. This low may bring up tropical moisture and instability into the windward and southeastern slopes of the Big Island, enhancing shower activity from Friday into next weekend. The American (GFS) model also shows windward Maui picking up additional shower activity by Saturday. Rainfall impacts for the eastern islands will to a large degree depend upon the strength and final track of this upper level low. Stay tuned for more details as the forecast time period grows shorter.

Aviation

Light to moderate trades strengthening through mid-week. Low cigs and SHRA should mainly impact windward and mauka locations. Brief MVFR conds can be expected in SHRA otherwise VFR conds should prevail.
AIRMET Tango is in effect for mod turb btn 130 and FL400 for the entire chain. With trades on the rise, AIRMET Tango may also be needed for mod low level turb over and downwind of terrain later today. Please see SIGMET Whiskey series for sev turb information.

Marine

Easterly trade winds steadily strengthened overnight, reaching moderate to strong levels early this morning. By Tuesday, fresh to strong breezes are expected across most waters as a surface ridge establishes itself to the north. Small Craft Advisory (SCA) conditions are expected for the windier waters around Maui County and the Big Island beginning this morning, with an expansion to additional waters by Tuesday due to stronger winds and building seas. These conditions are expected to persist through much of the week.
Surf along north and west-facing shores will increase throughout the day as a fresh north-northwest swell builds down the island chain. Overnight observations at offshore NDBC buoys northwest of Kauai indicated a rising trend in the 15-21 second bands before midnight. This trend is expected to continue today, with a peak likely occurring later today through Tuesday. Surf heights could approach low-end advisory levels this afternoon and potentially reach advisory thresholds tonight through Tuesday, especially if the swell exceeds predictions. A slight downward trend is expected during the second half of the week, with surf holding steady near or slightly below seasonal averages by Friday into the weekend.
Surf along south-facing shores will remain up today due to an out-of-season south swell, which will gradually subside by Tuesday. Seasonal conditions are expected to return midweek, with smaller southeast and south-southwest swells contributing to surf conditions.
Surf along east-facing shores will rise through the week as trade winds strengthen locally and expand upstream across the eastern Pacific.

Fire weather

Relative humidity (RH) levels will approach critical thresholds over some of the windier leeward areas as we adjusted moisture levels a bit lower using model blend solutions. Critical fire weather threats appear to be borderline over small portions of some of the Big Island leeward areas near Waimea and over portions of the leeward slopes of the Kohala Mountains on Tuesday and Wednesday afternoons. Overall RH values across the state still look to be the limiting factor, however minimum afternoon RH levels could still briefly drop below 50 percent during these windier periods. We will continue to closely monitor these wind and humidity levels as this weather pattern evolves through the week.

HFO Watches/Warnings/Advisories

High Wind Warning until 6 PM HST this evening for Big Island Summits.
Small Craft Advisory until 6 PM HST Wednesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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