Tropical cyclone formation is possible within the next week as two tropical waves in the Central and East Pacific show increasing odds of development, according to federal forecasters and local weather watchers.
Forecast centers reported early Sunday that a tropical wave about 1,000 miles east-southeast of the Hawaiian Islands is generating disorganized showers and thunderstorms. Environmental conditions are expected to support further development, and a tropical depression is likely to form in the coming days as the system tracks west-northwest across the Central Pacific.
Formation odds for this system are low through 48 hours at 30%, but forecasters place the chance of development at 90% over the next seven days.
Citizen forecaster Harry Durgin, who runs the Puna Weather public Facebook group, noted in an Aug. 8 update that the Madden-Julian Oscillation is moving through the Central Pacific and vertical wind shear is easing over the state. He said multiple forecast models are leaning toward low-pressure development and that very warm sea surface temperatures could support a stronger system. Durgin emphasized the uncertainty a week out, saying the system might fail to form, stay weak, pass south or east of the islands, or in a worst-case scenario cause significant impacts.
To the east, another tropical wave several hundred miles southwest of the southern tip of the Baja California Peninsula is also producing a broad area of disorganized convection. Conditions there favor gradual development as the disturbance moves slowly west-northwest to northwest across the western East Pacific. The probability of formation is 30% through two days and 60% through seven days.
Tropical cyclone formation monitoring and local impacts
National Weather Service forecasters in Honolulu said Saturday night that breezy trade winds will steer low clouds and showers into windward and mauka areas through midweek. A moisture plume skirting south of the state is expected to boost rainfall chances over the eastern end of the chain through Aug. 10.
Durgin added that a weak low passing south of Hawai‘i Island will draw a large swath of tropical moisture over the Big Island, keeping conditions humid with periods of heavy rain and light to moderate easterly trades through Monday, especially for Puna. Typical trade wind weather is expected to return Tuesday through Thursday, though very warm ocean temperatures will keep the air muggy. While somewhat drier conditions are anticipated from Aug. 11 to 13, scattered showers remain possible for Puna and East Hawai‘i with persistent trades.
Forecasters caution that the tropical disturbances need to be watched closely over the next several days for more organized development. Durgin flagged the Aug. 14 to 16 period as one to monitor for potential storm conditions and said he will post updates at least twice daily until the threat diminishes. He urged residents to stay informed as model guidance may shift day to day.
For official updates, track systems in the Central and East Pacific at the National Hurricane Center and Central Pacific Hurricane Center websites. Local forecasts, advisories, watches, and warnings are available from the National Weather Service Honolulu forecast office. Preparedness information can be found at Hawai‘i County Civil Defense, the Hawai‘i Emergency Management Agency, and the National Weather Service hurricane safety pages.
Related coverage: Hurricane Fausto enters Central Pacific, tracks west.
