Heads up Hawaii: Double trouble is headed your way in the form of two tropical cyclones.
The image above, acquired Monday (Aug. 4) by NASA’s Terra satellite, shows the situation: Hurricane Iselle to the left, and Tropical Storm Julio to the right. Both are expected to affect the Hawaiian Islands in the coming week.
As I write this late on Monday night, Iselle is a strong storm with winds over 130 miles per hour, qualifying her as a Category 4 cyclone. Iselle also has the distinction of being a very rare “annular” cyclone, according to Jeff Masters, chief meteorologist for Weather Underground. This means it features a thick eye wall and a dearth of spiral bands.
According to Masters:
Annular hurricanes are a subset of intense tropical cyclones that are significantly stronger, maintain their peak intensities longer, and weaken more slowly than average tropical cyclones . . . Only 4% of all hurricanes are annular hurricanes.
This closeup image of Iselle’s eye, acquired on Monday by the GOES-15 satellite, shows both the thick eye wall and features within the eye called mesovortices. Make sure to click on it to watch an animation from the Cooperative Institute for Meteorological Satellite Studies showing these features rotating within the eye.
Wind speeds in mesovortices can be even higher than they are in the eyewall itself. They tend to be most common when a tropical cyclone is undergoing rapid intensification.
Here’s the forecast for Hurricane Iselle, from the National Hurricane Center:
Iselle should retain its current annular characteristics during the next 12 hours or so, and thus only slow weakening is likely. After that time, enough of an increase in southwesterly vertical shear and the ingestion of drier and more stable air should disrupt the status quo and result in steadier weakening. Even further weakening should occur by the time the center of Iselle approaches the Hawaiian Islands in 48-72 hours, mostly as a result of a very dry air mass in which the storm will be moving.
But even though Iselle will likely have weakened to a tropical storm when reaches the area of the Hawaiian Islands, the storm can still cause mayhem in the form of torrential rainfall.
And following fast on her heels is Julio. Here’s the forecast track:
Right now, it looks like Julio will pass very close to Hawaii on Sunday night, and it could wind up being stronger than Iselle when it gets there. Time will tell.