Photo Credit: Jason Weingardt

West Kaua’i

Today: Sunny. Isolated showers in the morning. Highs around 88 near the shore to around 76 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear with isolated showers. Lows around 70 near the shore to around 61 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tuesday: Sunny. Isolated showers in the afternoon. Highs around 88 near the shore to around 76 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs 82 to 88. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 72. Northeast winds around 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 82 to 88. Northeast winds around 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 73 to 84 in the valleys to around 66 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 65 to 70 in the valleys to around 58 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Tuesday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 73 to 84 in the valleys to around 66 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 60 percent.

North Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 76 to 89. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Scattered showers. Lows 65 to 74. East winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 75 to 88. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny with scattered showers. Highs 73 to 85. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 65 to 76. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 73 to 85. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

High pressure north of the state will maintain breezy trade winds the next couple of days. Showers will favor windward coasts and slopes. Trades will slightly weaken around the middle of the week with a possible increase in weekend shower activity.

Discussion

The downstream pressure gradient from a 1031 mb high centered approximately 860 miles north northwest of Kauai remains tight enough across the region to maintain breezy to locally windy trade winds through Tuesday. The state will remain under the stabilizing influence of mid-level ridging as the islands reside along the southeasterly periphery of a 700 mb ridge positioned northwest of the area. Early morning radar and satellite imagery show fairly dry conditions with only widely scattered weak trade showers traveling across the isles. Expect these conditions to continue through the day with showers favoring windward exposures.
Higher 850-700 mb layer moisture advection assisting in deepening a more moist boundary layer Tuesday and Wednesday, in tandem with the emergence of a subtropical jet draped across the southern nearshore waters, should be the impetuses to increased shower coverage. Those communities that typically stay more wet than dry during normal summertime trades will likely pick up a few hundredths to tenths of an inch more rain through mid week. Aside from a few brief afternoon showers over the Kona slopes of Big Island or a stray windward cell making it over the ridgeline, leeward areas will primarily remain dry. Little to no movement of lower and upper ridging anchored north of the islands through Tuesday ensures breezy trades under partly to mostly cloudy windward skies/mostly to partly sunny leeward skies.
High pressure at all levels begins to transition east during the second half of the week. This will weaken the lower level pressure gradient enough to subtly suppress trade flow to more gentler magnitudes, although easterlies will still remain breezy along ridge lines and within valleys parallel to trade flow. Lowering mid to upper heights, with periodic ribbons of higher east moisture passing to the west, will increase late week shower frequency and areal coverage. An upper trough/cut-off low develops east of the islands from the middle of the week onward. This scenario may boost weekend into early week rain probabilities across more windward waters/exposures. The highest rainfall will likely be focused north of the island chain as the low moves north northwest of the state early next week.

Aviation

Breezy to locally windy trades will continue today, then gradually ease late tonight through Tuesday. Showery cloud bands embedded in the trade flow will produce periods of MVFR conditions across windward/mauka areas of each island, particularly through the overnight and early morning hours. Conditions will improve through the late morning and afternoon periods.
AIRMET Sierra remains in effect for tempo mountain obscuration for windward slopes of most islands, which will likely continue through the morning hours.
AIRMET Tango remains in effect for mod low-level turb over and downwind of island terrain due to the breezy trade winds. This AIRMET will continue through the day.

Marine

Surface high pressure centered roughly 950 nm north of the state will help to drive fresh to strong easterly trades today. The Small Craft Advisory has been extended until Tuesday morning, but trimmed back to only include the typical windier waters around Maui County and the Big Island. Trades weaken slightly Tuesday into mid week as the high moves east northeastward, away from the islands.
Surf along east-facing shores will remain rough and choppy today followed by a gradual downward trend during mid week as trades weaken slightly.
Surf along south-facing shores will be near or slightly below seasonal norms through Tuesday as a small, medium period, south swell continues to move through. Nearshore buoys showed swell energy peaking this morning in the 12-14 second range. However, this should be short-lived, with a downward trend expected by Tuesday night. More small, medium to long period, south swells will return Wednesday night through the remainder of the forecast period.
Nearly flat conditions along north-facing shores expected through mid day today. A small, medium period, northwest swell will bring tiny surf to north-facing shores late today through mid week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov