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Irma: Why It’s Too Early to Talk a U.S. Landfall

2 Sep 2017, 5:23 pm

By now there’s no doubt you’ve seen the hype. A potential landfall from Hurricane Irma in the coming week.

But before you jump on the bandwagon, there are a few things you should know.

Current Conditions

Irma is currently churning in the Atlantic as a category 2 storm. Strong, but not yet major hurricane status.

Forecast

In the comings days the storm is set to track just north of the Greater Antilles. The forecast cone gives us an idea over a breadth of possible paths the storm could take in the coming days as well as a general idea of strength of the storm.

There are many different model runs that go into creating an accurate forecast. Each with its own unique interpretation of the data. Different strengths and different paths, but when there is agreement between the models it usually means the forecast can be more accurate.

Below is an example of what we call an ensemble run, or more colloquially– spaghetti models. It just throws all of the runs on one map.
Notice how after a few days they start forecasting much different tracks.

This is the uncertainty in the forecast and it exists for good reason.

Long-Range Forecast

There are some major steering factors when it comes to Hurricane Irma in the coming week.

Two of the biggest factors are the Bermuda High and the Jet Stream over the U.S.

One possibility is that Irma stays entirely out to sea. This could easily happen with a weaker Bermuda High and a strong or deep trough in the Jet Stream.
This would be a very similar weather pattern to the one we saw this past week with fall-like temps across the eastern U.S.

The other possibility is that Irma moves toward the U.S. This scenario involves a strong Bermuda High and a weak trough in the Jet Stream.
Think warmer and clear days along the east coast.

As with any forecast, hurricanes are very difficult to predict more than a couple days out. Seemingly endless factors play into potential paths and strengths. Each compounding the factor of uncertainty as the forecast looks further into the future.
That is why simply looking at one map from one individual model run is never a good idea. In fact, during the day today the forecast path has changed drastically with each run of the models that has come in.

So as a word of caution, stay weather aware and always be prepared for the worst– but never put your faith in long-range forecasts. They’ll let you down more often than not.

For WeatherNation — Meteorologist Jeremy LaGoo

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