Potential rainfall from Calvin calls for 4-7 inches on Big Island, 1-4 inches elsewhere

Tropical Storm Calvin is nearing the Central Pacific Basin and is expected to be near the Hawaiian Islands by late Tuesday or early Wednesday, according to the latest update from the National Hurricane Center.

As of 5 p.m., the system had maximum sustained winds of 60 mph with higher gusts, and was moving west at 17 mph. Calvin was located about 1150 miles east of Hilo, on Hawaiʻi Island; 1220 miles ESE of Hāna, Maui; and 1255 miles ESE of Kahului, Maui.

The National Hurricane Center says storm total rainfall amounts of 4-7 inches are possible along windward areas of the Big Island of Hawaiʻi from Tuesday night into Thursday, with lower amounts of 1-4 inches elsewhere in the state. According to the NHC forecast, swells generated by Clavin are expected to begin reaching the Hawaiian Islands over the next couple of days.

The NHC reports that a Tropical Storm Watch may be required for portions of the main Hawaiian Islands tonight.

Latest time-of-arrival graphical forecasts indicate that the earliest reasonable arrival time for tropical-storm-force winds on the Big Island is Tuesday evening, according to the NHC. The latest NHC forecast indicates that some additional weakening is forecast during the next few days, but tropical-storm-force winds extend outward up to 90 miles from the center of the storm.

The National Weather Service says Tropical Storm Calvin is forecast to move close to, or over, the islands from Tuesday night through Wednesday night, bringing the potential for a period of locally strong winds, heavy rain, and high surf.

The NWS issued a forecast discussion on Sunday afternoon saying, “Overall rainfall may decrease slightly Monday and Monday night as subsidence ahead of Tropical Storm (TS) Calvin moves over the islands from the east.”

According to the NWS discussion: “The official forecast from the National Hurricane Center in Miami, Florida has been consistent in anticipating that the center of Calvin will move close to, or over, the Big Island Tuesday night and Wednesday, while producing tropical-storm-force winds in its northern semicircle. There is some uncertainty with the track and intensity forecast, and it is important to remember that impacts can occur well away from the center.”

Forecasters with the NWS say Calvin’s forward speed will be “fairly quick” when it is near the islands, “so the amount of time any one island experiences gusty winds and heavy rainfall will be somewhat limited (probably on the order of 12-18 hours). However, the potential for extreme rainfall rates will likely warrant the issuance of a Flood Watch, which is usually done with about a 48 hour lead time.”

“A return to a typical trade wind weather pattern is expected from Thursday into next weekend as the remnants of Calvin move quickly west away from the islands, likely as a trough,” according to the NWS.