Tropical cyclones span the enormous tropical Pacific from end-to-end, and several will likely strike land over the next week. Major Hurricane Iselle and Tropical Storm Julio stare down Hawaii, while Typhoon Halong threatens Japan. (Not to mention Tropical Depression Genevieve also struts along the lengthy storm runway, but will remain over the water.)
After reaching Category 4 intensity Monday, Hurricane Iselle has modestly weakened, but remains a major hurricane with maximum sustained winds of 125 mph.
It is classified as a rare “annular” hurricane due to several characteristics including its highly symmetric shape, large eye, and concentrated core of thunderstorms around the eye flanked by an abrupt cutoff and lack of spiral banding. Just four percent of hurricanes are annular, and they are known for their staying power, weakening more slowly under unfavorable conditions compared to conventional hurricanes.
Iselle is gradually forecast to lose its annular characteristics which should allow weakening to hasten before approaching Hawaii’s Big Island Thursday night. Intensity forecasts nevertheless vary significantly. Some models suggest Iselle will be a weak tropical storm at landfall, others a hurricane. Also, there is enough uncertainty in the track forecast that a direct hit on any of the Hawaiian islands isn’t guaranteed.
Irrespective of the uncertainties, Hawaiians should begin to think about hurricane preparations. Some sage words here from the National Hurricane Center:
Interests in the Hawaiian Islands should closely monitor the progress of Iselle. However, it is important not to focus too closely on the exact track and intensity forecasts because the average track error 72 hours out is about 100 miles, the average intensity error is about 15 kt. In addition, the hazards of a tropical cyclone can extend over a broad area well away from the center.
Tropical Storm Julio
If somehow Iselle misses or just skirts the Hawaiian islands, Tropical Storm Julio follows close behind. Or Hawaii could get hit back-to-back.
Since Monday, Julio has ticked up in intensity, with maximum sustained winds up to 60 mph from 45 mph. It is forecast reach hurricane intensity in the next 24 hours. The National Hurricane Center forecast suggests Julio will maintain hurricane intensity through the weekend. The track forecast indicates it will approach Hawaii late Sunday into Monday, but the cone of uncertainty is large and there’s some chance the storm could pass just north of the islands.
The prospect of back-to-back named storms striking Hawaii is unprecedented in records dating back to 1950. There have been cases in which two or more remnant storms and/or depressions have affected Hawaii in short succession, but direct strikes from two named storms in less than a week would be a first.
Of course, it’s very possible Iselle and/or Julio miss or skirt the islands or weaken below storm strength. But clearly, this is a unique, potentially hazardous situation Hawaii should monitor closely.
Working into the western Pacific basin, Typhoon Halong continues on a path towards Japan.
At one time a super typhoon (with peak winds over 150 mph), Halong has steadily weakened over the last 48 hours from increasing wind shear and cooler waters. Its maximum sustained winds are down to 95-100 mph. Little change in strength or a slight weakening is expected before Halong most likely makes landfall in southern Japan Friday.
Torrential rain and flooding is the primary concern from Halong when it comes ashore due to saturated ground from earlier rains. Notes Weather.com: “Shigeto, in the mountains of Kochi Prefecture, reported 1,297.0 millimeters (51.06 inches) of rain in just the first four and a half days of August, already making it the wettest August and second-wettest month overall since records began there in 1976.”
The Joint Typhoon Warning Center cautions there is large uncertainty in the track forecast, so the possible landfall zone is wide – ranging from the coast of South Korea to northeast Japan.