The first high surf warning of the winter season has been issued for the north and west shores of Niihau, Kauai, Oahu and Molokai, and the north shores of Maui, effective until Wednesday morning.

Surf of 22 to 26 feet is expected along north shores, while surf of 15 to 20 feet along west shores is expected today and tonight due to a large, north-northwest swell.

The National Weather Service said the swell hit Kauai at around sunrise and will travel down the isle chain from Oahu to Maui the rest of today. This warning-level surf will continue through tonight as it subsides. NWS expects to lower the warning to a high surf advisory once levels fall below the warning threshold.

Weather officials, meanwhile, warn of ocean water occasionally sweeping across portions of beaches, along with strong, breaking waves and rip currents, which make entering the ocean very hazardous. Anyone entering the water could face significant injury or death, officials warn.

This year’s first high surf warning arrived a little later than the usual arrival time of about Oct. 21 or so, but is not excessively late, according to NWS forecaster Derek Wroe.

Surf on other shores, meanwhile, remains low, at 1 to 3 feet for south shores today and Wednesday, and flat to 2 feet today for east shores, then rising to 2 to 4 feet on Wednesday.

Forecasters expect tradewinds to return and strengthen Wednesday into Friday, which will gradually build surf along east shores to moderate levels. A moderate pulse from the north-northeast Wednesday may also add an additional foot or two to exposed, north shores.

The state Health Department’s clean water branch has issued brown water advisories for various parts of Oahu’s North Shore as a result of high surf bringing coastal waters above the normal high-water mark, including Haleiwa Beach Park, Chun’s Reef and Laniakea.

Heavy river flows due to rains have also resulted in brown water advisories for Punaluu and Kaluanui beach parks on Oahu.

The public is advised to stay out of coastal waters that appear brown due to possible runoff containing pesticides and other chemicals, as well as animal fecal matter, pathogens, and debris. If the water is brown, stay out, officials said.

A small craft advisory is also in effect for most waters along the island chain — from northwest of Kauai to windward of Hawaii island — through 6 a.m. Wednesday.