A pair of tropical systems in the eastern Pacific are both following a general path leading towards Hawaii over the next week.

Dangerous Hurricane Iselle, packing 140 mph sustained winds, is 1200 miles east of the Big Island and is forecast to sweep through the Hawaiian islands Friday into Saturday but as a much weaker storm.

Further east and less menacing for the moment, tropical storm Julio, is roughly twice that distance away. If it affects Hawaii, it would probably be about a week from now.


The extremely powerful Hurricane Iselle attained category 4 status this morning. The storm has a very impressive satellite presentation with textbook symmetry and a well-defined eye.


As Iselle moves over cooler water over the next couple of days, it is forecast to slowly lose strength. By the time it reaches the Hawaiian islands late this week, the National Hurricane Center forecasts its peak winds to drop to 50-70 mph – or to moderate tropical storm levels. However, intensity forecasts vary among models and are fairly uncertain, so Hawaii could plausibly deal with anything from a formidable hurricane to a weak tropical storm.

Iselle intensity forecast from group of models (UCAR)

The National Hurricane Center seems fairly confident the storm won’t miss, per its technical discussion:

…a mid-level high is forecast to develop and strengthen between Hawaii and California, forcing Iselle to turn west-northwestward and accelerate as it approaches and moves near the Hawaiian Islands. The track guidance has been stable and tightly clustered for a few cycles now.

(National Hurricane Center)


Compared to Iselle, Julio is much less organized. Strong wind shear from the northeast is pushing thunderstorms west of the storm center. Its peak winds are just 45 mph. This wind shear is likely to keep the storm from substantially intensifying over the next day.


But forecast models suggest a window for intensification midweek, and unanimously predict it to become a hurricane by Wednesday.

Julio intensity forecast from group of models (UCAR)

Later this week – like Iselle – the storm may begin to weaken as it encounters cooler water. If it tracks over the same area as Iselle (which is possible later this week), it may also pass over the cool water’s in Iselle’s wake, which would further limit its intensity.

Iselle could impact Hawaii in about a week. Forecast models generally track the storm very close to Hawaii next Monday and Tuesday, but I should stress a week is an eternity in forecasting the position of a small weather system like a tropical cyclone.

Track forecast for Hurricane Iselle and Tropical Storm Julio over next week from European model (WeatherBell.com)

Slight changes in Julio’s forecast track could easily place Hawaii out of harm’s way.

Hurricanes and Hawaii

The prospect of two tropical cyclones hitting Hawaii in the same week should have folks on the islands on alert.

Hurricane impacts in the Hawaiian islands are relatively rare. Since records have been kept in 1950, just five hurricanes have caused significant damage and fatalities there.

Related: Hawaiian hurricanes: Hardly common, but occasionally havoc-wreaking

Tropical storms, however, are more common. Wikipedia lists the numerous tropical storms which have affected Hawaii in recent decades. Examples of back-to-back tropical cyclones sweeping through Hawaii in less than a week’s time are few.  In 1992, Hawaii was struck by Hurricane Iniki and Tropical Depression Orlene September 11 and 14, respectively.  Between July 14 and 24, 1994, three tropical cyclones (or their remnants) passed in the vicinity of Hawaii: Daniel, Emilia, and Fabio.