Hilo

Tonight: Mostly cloudy. Scattered showers in the evening, then occasional showers after midnight. Lows 62 to 68 near the shore to 50 to 56 at 4000 feet. North winds up to 10 mph shifting to the west around 10 mph after midnight. Chance of rain 90 percent.

Tuesday: Partly sunny. Scattered showers in the morning, then numerous showers in the afternoon. Highs 78 to 83 near the shore to 63 to 68 at 4000 feet. Northwest winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 60 percent.

Tuesday Night: Cloudy with occasional showers. Lows 61 to 68 near the shore to 50 to 57 at 4000 feet. North winds up to 10 mph. Chance of rain 90 percent.

Kona

Tonight: Mostly cloudy in the evening then clearing. Isolated showers. Lows around 70 near the shore to 44 to 50 near 5000 feet. Light winds becoming east up to 10 mph after midnight. Chance of rain 20 percent.

Tuesday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 81 to 86 near the shore to around 66 near 5000 feet. Light winds. Chance of rain 30 percent.

Tuesday Night: Mostly cloudy with scattered showers in the evening, then mostly clear with isolated showers after midnight. Lows around 70 near the shore to 45 to 52 near 5000 feet. Light winds. Chance of rain 40 percent.

Waimea

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 62 to 71 near the shore to 52 to 59 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Tuesday: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs 63 to 82. East winds 10 to 25 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy. Showers likely in the evening, then scattered showers after midnight. Lows 60 to 70 near the shore to 53 to 61 near 3000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Kohala

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 62 to 71 near the shore to 52 to 59 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Tuesday: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs 63 to 82. East winds 10 to 25 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy. Showers likely in the evening, then scattered showers after midnight. Lows 60 to 70 near the shore to 53 to 61 near 3000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

South Big Island

Tonight: Mostly cloudy in the evening then becoming mostly clear. Breezy. Isolated showers. Lows around 71 near the shore to around 50 near 5000 feet. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny. Breezy. Scattered showers in the afternoon. Highs around 85 near the shore to around 66 near 5000 feet. East winds 10 to 20 mph. Chance of rain 30 percent.

Tuesday Night: Partly cloudy. Isolated showers in the evening. Lows around 71 near the shore to around 50 near 5000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Puna

Tonight: Mostly cloudy. Scattered showers in the evening, then occasional showers after midnight. Lows 62 to 68 near the shore to 50 to 56 at 4000 feet. North winds up to 10 mph shifting to the west around 10 mph after midnight. Chance of rain 90 percent.

Tuesday: Partly sunny. Scattered showers in the morning, then numerous showers in the afternoon. Highs 78 to 83 near the shore to 63 to 68 at 4000 feet. Northwest winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 60 percent.

Tuesday Night: Cloudy with occasional showers. Lows 61 to 68 near the shore to 50 to 57 at 4000 feet. North winds up to 10 mph. Chance of rain 90 percent.

Waikoloa

Tonight: Mostly cloudy in the evening then becoming mostly clear. Isolated showers. Lows 68 to 74 near the shore to 47 to 52 above 4000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny. Isolated showers in the afternoon. Highs 82 to 87 near the shore to 63 to 71 above 4000 feet. Southeast winds up to 10 mph shifting to the north in the afternoon. Chance of rain 20 percent.

Tuesday Night: Partly cloudy with isolated showers. Lows around 72 near the shore to 48 to 53 above 4000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Breezy trade winds will gradually ease this week, becoming light and variable. Clouds and showers will favor windward areas the next couple of days, but shower coverage and frequency will gradually diminish thereafter as the island atmosphere stabilizes. Mainly dry conditions and light winds are expected from Thursday into the weekend, although a weak front may bring increased showers by Sunday.

Discussion

Changes to the recent windy and locally wet weather pattern are expected, with much lighter winds and less rainfall anticipated for the second half of the week.
A 1033 mb high far NE of the islands continues to support a fairly strong and gusty trade wind flow, delivering scattered stable and showery low clouds from the E. A closed low aloft lies over the island chain, and its associated mid-level cold pool (500 mb temp of -13C) has led to some modest destabilization of the island atmosphere. Afternoon soundings and radar wind profiles indicate that the mixed layer extends as high as 8-10 thousand feet, high enough to allow a few of the incoming showers to be briefly heavy.
Latest visible satellite images indicate reduced low cloud and shower coverage immediately upstream of the islands, with mid- and upper-level clouds streaming NE over portions of the Big Island. So, despite the modest instability, the expectation is that shower coverage will be somewhat limited this evening, with a diurnal increase in windward showers expected later tonight. Guidance has initialized well with an E-W showery cloud band along 22N between 146W and 152W, or about 400 miles E of the islands, and depicts this moisture arriving Tuesday afternoon and evening, fueling an increase in windward showers.
The high to the NE will move S and weaken in the short term, splitting into two centers by Tuesday, with one being a 1020 mb high due N of the islands. This high will support moderate trade winds for a couple of days, then move S and weaken by Friday as low pressure develops to the N. Guidance indicates a surface ridge will be just N of, or over, the islands by Friday – likely leading to light and variable winds over land. Current forecast grids lean toward ECMWF guidance, which moves the ridge over the islands a little more quickly than the GFS. A weak front (or fronts) associated with the low may bring increased showers as they move over the islands late in the weekend and early next week, but forecast confidence is low due to model differences.
The low aloft will linger in place through Tuesday, then move SE and weaken as a ridge builds over the islands from the W. The island atmosphere will stabilize as the low departs, and trade shower coverage, frequency and intensity will diminish as the subsidence inversion lowers. The moderate trades will likely still deliver a few windward showers, especially night and morning, but rainfall totals are expected to be low. The ridge aloft will likely weaken as a trough passes N of the islands next weekend.

Aviation

Trade winds will diminish gradually through midweek. Expect brief MVFR ceilings and visibilities within showers across windward and mauka areas, with showers reaching leeward areas at times where VFR conditions should prevail.
AIRMET Tango remains in effect for moderate low-level turbulence over and downwind of island terrain. This AIRMET will likely remain in effect through tonight. No other AIRMETS are in effect or expected.

Marine

High pressure centered far northeast of the islands will continue to support locally strong trade winds through Tuesday. Winds will then weaken through the rest of the week as the high weakens and moves southward. Additionally, buoy observations and guidance indicates that rough and choppy 10 foot seas continue across windward waters from Oahu eastward. Therefore, the Small Craft Advisory (SCA) has been extended through tonight, and then will be scaled back to the typically windy waters and channels of Maui County and the Big Island by early Tuesday morning.
Surf along east-facing shores is on the decline, but will remain rough and choppy through tonight. With surf heights continuing to drop, the High Surf Advisory (HSA) for east facing shores has been cancelled.
The current small, medium period northwest (320 degree) swell will continue to decline tonight. However, a similar pulse from the northwest is possible late Wednesday night into Thursday, providing a small boost in north shore surf. A larger medium-period northwest swell is expected this weekend, as well as a moderate northeast swell. This combination of swells could result in advisory-level surf for north and west facing shores this weekend.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov