Why It’s So Hard to Predict Hurricane Irma’s Path

  • Massive effort underway to map weather systems over U.S.
  • Changing weather patterns will determine Florida’s fate

Irma in 'Perfect Storm' Conditions, Says Meteorologist

Predicting Hurricane Irma’s path over the next few days will be harder thanks to shifting, high-elevation weather patterns that will determine whether Florida takes a direct hit or is spared the full wrath of the monster storm.

And with satellites, radar, jet aircraft and high-speed computers at hand, forecasters still rely on old-fashioned weather balloons to determine where Irma will wreak the most havoc. National Weather Service offices across the U.S. have doubled the number of data-gathering balloons launched daily to try and unlock the secrets of systems that could mean the difference between salvation and devastation across Florida.

Hurricanes don’t move under their own power, so predicting what they will do requires knowing what larger, constantly moving high pressure ridges and low pressure troughs are up to. Hydrogen filled balloons, a method that became routine more than 80 years ago, sample the air every 15 to 20 feet on their journey about 22 miles (35 kilometers) high, sending real-time data back to the ground and providing a crucial tool for forecasters.

“Hurricanes are relatively easy to predict when the steering effects are constant,” said Jeff Masters, co-founder of Weather Underground in Ann Arbor, Michigan. “When there is a transition to a new influence then the forecast gets more difficult.”

Irma, which swept over islands in the Caribbean early Wednesday with a potential landfall in Florida this weekend, will pass through separate high-level systems along the way, complicating the job for forecasters. The uncertainty can be seen in the National Hurricane Center’s estimates of Irma’s path, which can vary from day to day.

The outlooks resemble elongated blobs that get wider the farther out in time they go, a configuration known as “the cone of uncertainty.” At the far end of the forecasts, which extend out five days, the margin of error can be on the order of 225 miles, or about the distance between New York and Boston.

Turn North

“The latest data suggests an earlier turn to the north which means a reduced chance of catastrophic damage on Florida’s Gulf Coast side,” said Todd Crawford, lead meteorologist with The Weather Company in Andover, Massachusetts.

Of course that means “increased chances of really bad things” on the Miami side of the state, he said. There is even a possibility that it could miss Florida altogether and go on to crash into either South Carolina or North Carolina next week.

Slight variations in any big storm’s path can test the mettle of commodity traders. Orange juice futures fell Wednesday after gaining 6.2 percent Tuesday as the storm threatens the largest supplier after Brazil. Cotton was little changed, while natural gas slid Tuesday on speculation the storm will wipe out demand for the power-plant fuel.

Irma boasted top winds of 185 miles (300 kilometers) an hour, making the system a Category 5, the highest measure on the five-step Saffir Simpson scale as of 1 p.m. New York time. It was about 90 miles east of San Juan, Puerto Rico.

Irma is being pushed west by a high-pressure ridge over the Atlantic, according to the hurricane center, a trend that’s expected to persist for two or three days.

Florida Strike

After that, a low-pressure trough crossing the U.S., will “erode” the high’s influence and pull Irma to the north or northwest. As of Wednesday, the forecast track, based on the mean of the world’s best models predicted a strike into south Florida.

National Weather Service offices across the U.S. are scrambling to pin down the details of that low-pressure trough and what it will do as it moves east, said Masters, who once flew into hurricanes as a meteorologist with the National Oceanic and Atmospheric Administration.

Balloons are being launched every six hours, instead of the usual twice a day schedule, at 49 offices from the Great Plains to the Atlantic Coast and in Puerto Rico, Maureen O’Leary, spokeswoman for the agency said.

— With assistance by Sophie Caronello

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