Calvin has likely peaked in intensity; impacts for Hawaiʻi could include wind, rain and surf

Hurricane Calvin has likely peaked in intensity according to the National Hurricane Center. The system, which is currently in the East Pacific, has maximum sustained winds near 100 mph and is forecast to continue weakening through early next week. It was downgraded to a Category 2 hurricane (winds of 96-110 mph) overnight.

Calvin is currently expected to move into the Central Pacific late Sunday as a tropical storm. The National Weather Service says Calvin is forecast to pass very close to, and possibly over the islands from Tuesday night through Wednesday evening, bringing the potential for locally strong wind gusts, flooding rain, and high surf.

According to the NWS, the latest forecast indicates Calvin may move near the main Hawaiian Islands as a weakening tropical storm Tuesday night or Wednesday. It was last located about 1750 miles ESE of the Hilo, 1820 miles ESE of Hāna and 1855 miles ESE of Kahului, and was moving WNW at 16 mph.

As of 5 a.m. on July 15, the center of Hurricane Calvin had hurricane-force winds extending outward up to 35 miles from the center and tropical-storm-force winds extending outward up to 125 miles, the National Hurricane Center reports.

The National Weather Service says some questions remain as to the intensity as Calvin approaches the Hawaiian Islands, but vertical wind shear is expected to increase as it nears, with Calvin on a “gradual weakening trend during its closest point of approach.”

Like most systems approaching Hawaiʻi from the east, the NWS says the strongest winds are expected to be in the northern semicircle of the system. 

“Considering typical forecast track errors, it remains too soon to be specific as to where (and what – if any) impacts occur over land, which will be highly dependent on the track,” according to the NWS. “If the center were to pass north of the islands, most of the strong winds would remain offshore, with a more southerly track potentially putting the islands in a stronger wind field.”

Forecasters with the National Weather Service remind the public that tropical cyclones can bring a “triple threat” of strong winds, heavy rainfall and high surf. The NWS says a Flash Flood Watch may be issued for parts (or all of) the state early next week. 

The NWS issued a detailed forecast discussion indicating that 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.”

On the water, the NWS reports that “an upward trend in surf is expected along east facing shores early next week due to the arrival of a swell, which is being generated “by the captured fetch associated with Hurricane Calvin.”

“There is a possibility that some east facing shores, such as the Big Island or Maui, may have a brief period of surf reaching the High Surf Warning criteria in the Tuesday night / Wednesday morning time frame based on the latest wave model guidance,” according to the NWS.