Honolulu, Aug 2 (IANS): The US National Weather Service (NWS) has issued weather alerts for Hawaii, as two tropical cyclones were passing south of the archipelago back-to-back over the next few days.

The NWS issued a Tropical Storm Warning on Thursday evening, downgraded from a Hurricane Warning posted four hours earlier, reports Xinhua news agency.

Tropical Storm Erick moved westward into the southeastern waters of Hawaii late Thursday. It gradually weakened from a hurricane before passing within about 321 km south of the Big Island, Hawaii.

Tropical Storm Flossie, also on a westward itinerary, will enter the east Hawaiian waters Sunday, the NWS reported.

The agency forecasted that Flossie would weaken too. However, both storms would enhance rainfall and churn up high surf in the Hawaii archipelago.

A flash flood watch was issued for the Big Island from Thursday to Saturday. A high surf warning is also in effect for east-facing shores of the island, some of which could see waves up to 20 feet high, making "entering the water very hazardous", said the NWS.

Parts of Maui island and Big Island could encounter up to 48 kph of winds and 72 kph of gusts.

According to the NWS, tropical cyclone activity in the eastern part of the North Pacific Ocean has been below average so far in 2019.