Hilo

Today: Mostly sunny with isolated showers. Highs 81 to 87 near the shore to 68 to 75 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 64 to 73 near the shore to 56 to 61 at 4000 feet. North winds up to 20 mph. Chance of rain 40 percent.

Tuesday: Breezy. Partly sunny with scattered showers in the morning, then cloudy with numerous showers in the afternoon. Highs 80 to 86 near the shore to 67 to 75 at 4000 feet. North winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Gusts up to 45 mph. Chance of rain 70 percent.

Kona

Today: Mostly sunny with isolated showers. Highs 84 to 89 near the shore to around 73 near 5000 feet. West winds up to 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows around 74 near the shore to 52 to 58 near 5000 feet. Light winds. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 84 to 91 near the shore to around 75 near 5000 feet. West winds up to 10 mph. Chance of rain 50 percent.

Waimea

Today: Breezy. Mostly sunny with isolated showers. Highs 66 to 85. East winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Windy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 65 to 73 near the shore to 57 to 64 near 3000 feet. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 40 percent.

Tuesday: Tropical storm conditions possible. Partly sunny with scattered showers. Highs around 81 near the shore to 70 to 80 near 3000 feet. Northeast winds 10 to 35 mph. Gusts up to 55 mph increasing to 65 mph in the afternoon. Chance of rain 50 percent.

Kohala

Today: Breezy. Mostly sunny with isolated showers. Highs 66 to 85. East winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Windy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 65 to 73 near the shore to 57 to 64 near 3000 feet. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 40 percent.

Tuesday: Tropical storm conditions possible. Partly sunny with scattered showers. Highs around 81 near the shore to 70 to 80 near 3000 feet. Northeast winds 10 to 35 mph. Gusts up to 55 mph increasing to 65 mph in the afternoon. Chance of rain 50 percent.

South Big Island

Today: Breezy. Mostly sunny with isolated showers. Highs around 86 near the shore to around 70 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Breezy. Isolated showers in the evening. Lows around 74 near the shore to around 54 near 5000 feet. Northeast winds up to 20 mph in the evening becoming light. Chance of rain 20 percent.

Tuesday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 86 near the shore to around 71 near 5000 feet. West winds up to 10 mph. Chance of rain 40 percent.

Puna

Today: Mostly sunny with isolated showers. Highs 81 to 87 near the shore to 68 to 75 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 64 to 73 near the shore to 56 to 61 at 4000 feet. North winds up to 20 mph. Chance of rain 40 percent.

Tuesday: Breezy. Partly sunny with scattered showers in the morning, then cloudy with numerous showers in the afternoon. Highs 80 to 86 near the shore to 67 to 75 at 4000 feet. North winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Gusts up to 45 mph. Chance of rain 70 percent.

Waikoloa

Today: Mostly sunny. Breezy. Isolated showers in the morning. Highs 85 to 91 near the shore to 69 to 77 above 4000 feet. North winds up to 15 mph increasing to up to 25 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Breezy. Isolated showers in the evening. Lows around 75 near the shore to around 56 above 4000 feet. East winds up to 25 mph with gusts to 45 mph. Chance of rain 20 percent.

Tuesday: Tropical storm conditions possible. Mostly sunny. Isolated showers in the afternoon. Highs 85 to 91 near the shore to 71 to 77 above 4000 feet. Northeast winds up to 30 mph with gusts to 55 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A high pressure ridge north of the Hawaiian Islands will keep moderate to breezy trade winds in the forecast today with wind speeds increasing from tonight into Tuesday as Tropical Storm Calvin approaches the state. Calvin will likely move into the eastern half of the state from Tuesday night into Wednesday morning near the Big Island, then passing on a westerly track south of Maui County, Oahu and Kauai County. Strong winds, heavy rain and high surf will likely impact some of the islands with this storm. Breezy trade winds and more stable conditions will fill in behind Calvin on Thursday as it weakens and passes farther westward away from the islands.

Discussion

Satellite imagery this morning shows a weak low level trough passing just north of the island chain with some unstable clouds that will enhance shower activity mainly over windward and mountain areas of each island this morning. Tropical Storm Calvin located roughly 900 miles east of Hilo, Hawaii remains on a high confidence westward track into the Hawaiian Islands over the next three days.
The latest forecast from the Central Pacific Hurricane Center in Honolulu, Hawaii shows Calvin will continue to weaken as it passes over cool waters, draws in more stable drier air, and encounters increasing vertical wind shear. Weather and water impacts are likely, especially for the eastern half of the state, as Calvin approaches and moves through the Hawaii region from Tuesday through Wednesday. A Tropical Storm Watch was issued for the Big Island and surrounding coastal waters, with Tropical Storm impacts possible from Tuesday afternoon through Wednesday afternoon. A Flood Watch was also issued for the same time period for all islands in Maui and Hawaii Counties. The potential for significant weather and water impacts from Calvin may extend far from the center of the Tropical Storm.
Two main factors that will limit our exposure to these weather and water impacts are: Tropical Storm Force winds are weakening as the storm approaches the state due to less favorable environmental conditions, and the forward speed of the system is fairly quick limiting the amount of time over any island. Strong winds and heavy rainfall potential will probably be limited to around 12 to 18 hours for any one location. The earliest reasonable arrival time for Tropical Storm force winds for the Big Island is around Tuesday evening.
Since the public and marine forecasts for Hawaii are highly dependent on the tropical cyclone bulletins issued at 11 am/pm and 5 am/pm HST, our regularly scheduled forecast issuances will be issued shortly after these bulletins are released.
Trade winds will fill by Thursday as Calvin weakens and passes westward away from the island chain.

Aviation

Ridging to the northeast of the state will allow for moderate to locally breezy trades to persist through the remainder this morning and into the afternoon. Some modest low level moisture will get caught up in the flow and produce scattered showers along the windward coasts with isolated activity elsewhere. There may be brief periods of MVFR ceilings and visibility associated with these showers.
In the extended range, Tropical Storm Calvin is forecast to continue moving closer to the Hawaiian Islands over the next few days. The latest forecast track has the storm passing over or near the Big Island late Tuesday night into Wednesday. All interests should continue to monitor the forecast for the latest updates on Calvin and potential aviation impacts later this week.
AIRMET TANGO remains in effect below 9000 ft over and immediately south through west of mountains on all islands due to tempo moderate turbulence.

Marine

Tropical Storm Calvin, located 800 nautical miles east of Hilo, Hawaii, is tracking west at 17 knots. Calvin is forecast to enter the eastern offshore waters Tuesday, then track near or over the Big Island and its surrounding waters late Tuesday into Wednesday. Calvin will continue westward Wednesday as it weakens, while passing south of the smaller islands. A return of a more typical trade wind pattern is expected Thursday through the weekend.
A Tropical Storm Watch is now in effect for all Big Island waters. A Gale Watch is now in effect for the Pailolo and Maalaea Bay waters Tuesday afternoon through Wednesday.
Elsewhere, fresh to strong easterly winds will become strong statewide Tuesday night through Wednesday as Calvin passes to the south. This will translate to Small Craft Advisory conditions.
Coastal impacts associated with Calvin will include rapidly building surf for exposed windward coasts Tuesday night through Wednesday, that will potentially exceed the advisory level as it peaks. The best chance for a warning will be along east facing shores of the Big Island Tuesday night through early Wednesday. Although confidence is low, some minor overwash and erosion can't be ruled out for exposed low-lying coastal areas as the surf peaks Tuesday night for windward coasts on the Big Island.

HFO Watches/Warnings/Advisories

Flood Watch from Tuesday evening through Wednesday afternoon for Molokai, Lanai, Kahoolawe, Maui and the Big Island.
Tropical Storm Watch for Big Island.
Tropical Storm Watch for Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 PM HST Wednesday for Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters.
Small Craft Advisory until 2 PM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Gale Watch from Tuesday afternoon through Wednesday afternoon for Maalaea Bay, Pailolo Channel.

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Data Courtesy of NOAA.gov