Hilo

Today: Mostly cloudy with scattered showers. Highs 79 to 84 near the shore to around 71 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows 64 to 70 near the shore to around 53 at 4000 feet. North winds 10 to 15 mph shifting to the west after midnight. Chance of rain 70 percent.

Thursday: Mostly cloudy. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 79 to 84 near the shore to around 71 at 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Kona

Today: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 85 near the shore to around 69 near 5000 feet. West winds 10 to 15 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 70 to 75 near the shore to around 55 near 5000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Thursday: Partly sunny. Scattered showers in the afternoon. Highs around 84 near the shore to around 68 near 5000 feet. Southwest winds around 10 mph shifting to the north in the afternoon. Chance of rain 40 percent.

Waimea

Today: Breezy. Mostly cloudy with scattered showers. Highs around 80 near the shore to 68 to 78 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 63 to 68 near the shore to 51 to 61 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Thursday: Breezy. Mostly cloudy with scattered showers. Highs 77 to 82 near the shore to 68 to 78 near 3000 feet. East winds 15 to 25 mph. Chance of rain 50 percent.

Kohala

Today: Breezy. Mostly cloudy with scattered showers. Highs around 80 near the shore to 68 to 78 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 63 to 68 near the shore to 51 to 61 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Thursday: Breezy. Mostly cloudy with scattered showers. Highs 77 to 82 near the shore to 68 to 78 near 3000 feet. East winds 15 to 25 mph. Chance of rain 50 percent.

South Big Island

Today: Breezy. Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 83 near the shore to around 67 near 5000 feet. East winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 67 to 73 near the shore to around 53 near 5000 feet. East winds 10 to 25 mph. Chance of rain 20 percent.

Thursday: Partly sunny. Breezy. Scattered showers in the afternoon. Highs around 83 near the shore to around 66 near 5000 feet. East winds 10 to 25 mph. Chance of rain 40 percent.

Puna

Today: Mostly cloudy with scattered showers. Highs 79 to 84 near the shore to around 71 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows 64 to 70 near the shore to around 53 at 4000 feet. North winds 10 to 15 mph shifting to the west after midnight. Chance of rain 70 percent.

Thursday: Mostly cloudy. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 79 to 84 near the shore to around 71 at 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Waikoloa

Today: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs around 85 near the shore to 68 to 76 above 4000 feet. North winds up to 15 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Breezy. Isolated showers after midnight. Lows 69 to 74 near the shore to 49 to 59 above 4000 feet. Southeast winds 10 to 20 mph decreasing to up to 20 mph after midnight. Gusts up to 40 mph. Chance of rain 20 percent.

Thursday: Breezy. Partly sunny in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 85 near the shore to 67 to 75 above 4000 feet. North winds 10 to 20 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds will focus low clouds and showers over windward and mauka sections through this weekend. Brief trade showers may be transported over to the leeward sections of the smaller islands, especially during the late night and early morning hours. Clouds and isolated showers will also likely develop over some upslope sections of the leeward Big Island each afternoon.

Discussion

A broad 1032 mb surface high centered near 39N 157W, or about 1225 miles north of Honolulu, is dominating the local weather across the main Hawaiian Islands early this morning. The tight pressure gradient south of this feature is maintaining breezy trade winds across the island chain. Elsewhere, the leading edge of a large area of broken low clouds with embedded scattered showers, which is remnant moisture from a dissipated frontal boundary, is evident about 435 miles northeast of Hilo. This leading edge has been moving toward the west-southwest at about 15 mph. Loops of water vapor satellite imagery show an upper- level low centered near 23N 156W, or about 210 miles northeast of Honolulu. This feature has been moving slowly toward the west- southwest. There is also mid-level trough just west of Kauai that has been moving slowly westward.
The upper-level low appears to have started weakening the trade wind inversion across the eastern islands overnight. At the same time, low-level moisture is being transported into the area by the relatively strong low-level trade wind flow. As a result, scattered to broken low clouds with embedded isolated showers are evident in satellite imagery and radar reflectivity data just upstream of Maui and the Big Island. There are also scattered low clouds and a few light showers just upstream of the islands from Molokai to Kauai.
The forecast guidance shows the surface high will shift slowly southeast to a position far north-northeast of the islands during the next few days. At the same time, the upper-level low will move down closer to the islands There may be a slight weakening of the trade winds later today and tonight, but they will likely strengthen again from Friday into the weekend.
The close proximity of the upper-level low to the state will likely cause additional weakening of the trade wind inversion. Therefore, expect some enhancement of the low clouds and trade showers through Thursday. Most of the low clouds and showers will favor windward and mauka sections. However, there may be brief showers over some leeward areas of the smaller islands, especially during the late night and early morning hours. In addition, clouds and spotty showers will also likely develop over upslope sections of the leeward Big Island each afternoon, and then continue into the early evening hours.
As the upper-level low departs the region later this week, there may be a gradual increase in atmospheric stability over the state. The forecast models appear to show another area of increased moisture moving into the islands from late Friday into Saturday, so low clouds and showers may increase again over windward and mauka areas heading into the weekend. Expect a slight drying trend from Sunday into early next week, but some trade showers will likely continue along windward facing slopes.

Aviation

Coverage of light to moderate showers is low but increasing early this morning. The deepest moisture remains just upstream of the area and will work across the state through today. The deepest moisture and subsequent greatest coverage of showers will likely occur over Windward Maui and Molokai this morning followed by Oahu and Kauai this afternoon into this evening. The land breeze has inhibited inland penetration of showers for Windward Big Island, but the onset of diurnal heating later this morning should allow for a solid push of clouds and showers there as well. Instances of MVFR have been limited thus far, but AIRMET Sierra for mountain obscuration may eventually be needed for some windward zones as the day progresses.

Marine

The overnight ASCAT pass showed Small Craft Advisory (SCA) level winds continuing over the Alenuihaha Channel and around South Point on the Big Island. The high resolution models showed the winds over the remaining waters would be below SCA levels today, and so have dropped the other areas from the SCA. The SCA for the typical windier waters near Maui County and the Big Island has been extended through tomorrow night with this package. The ridge to the north of the islands is expected to remain in place through the end of the week, maintaining this moderate to locally strong trade wind pattern over the coastal waters. Easterly winds over the offshore waters will also continue, with the lightest winds over the northern offshore waters closer to the ridge.
The locally generated wind waves from the trades will continue to bring rough, choppy surf to east facing shores through the week. The current small, west- northwest swell will continue to decline today and tonight, with a slightly larger, and longer period, northwest swell arriving tomorrow, and continuing through the weekend. Background south swells will continue to keep small surf heights along south facing shores today. A slightly larger, long period southwest swell will arrive late tomorrow, helping to boost south shore surf through next weekend.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov