Things To Know Before Hurricane Season

How and whether a hurricane will develop gets a lot of attention. What matters most, though, is where it's headed.

Hurricanes are steered by wind flow through a deep layer of the atmosphere up to the level of the jet stream, much like a steering wheel does the same for your vehicle.

Here are some things meteorologists look for in these weather patterns to decipher whether a hurricane is a significant mainland U.S. threat, or simply likely to stay over the open Atlantic Ocean.

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Mainland US Threat Pattern

- Hurricanes that strike the mainland most often first become hurricanes in the Caribbean Sea, Gulf or near the Southeast coast, as we discussed in a previous article.

- They tend to develop later after moving off Africa as tropical waves and usually farther south in the tropical Atlantic Ocean.

- Stronger, more expansive high pressure over the central Atlantic known as the Bermuda-Azores high acts as a northern wall, forcing the storm to track westward longer, eventually bringing it closer to land.

- Lacking a significant southward dip in the jet stream in the eastern U.S., the system can't turn sharply north and northeast in time to avoid some part of the U.S. East Coast or Gulf Coast. Sometimes that jet stream dip arrives either too late, or simply, bypasses the storm altogether.

Recent Example: Isaias

- In 2020, Isaias battled interaction with land – Hispaniola – wind shear and dry air.

- But the Bermuda-Azores high was just strong enough and the jet stream's southward plunge over the Mississippi Valley was too far west.

- So, instead of curling sharply out to sea, Isaias raked up the Eastern Seaboard from the Carolinas to upstate New York with damaging winds, heavy rain and storm surge flooding.

Lower US Threat Pattern: The "Recurve"

- Most hurricanes that develop soon after moving off western Africa - known as Cabo Verde hurricanes - don't make it to the mainland U.S. But the few that do make it are almost always very destructive.

- Hurricanes starting off farther north in the eastern or central Atlantic have a better chance of eventually curling away from the mainland U.S. since they have more latitude to start with.

- But in this scenario, high pressure to the storm's north is weaker and less expansive, more confined to The Azores rather than Bermuda.

- There can also be a stronger southward dip in the jet stream near or along the U.S. East Coast.

- This configuration forces a hurricane to curl north, then northeast – known as recurving – sooner, steering it away from the East Coast into the open ocean.

- Occasionally, one of these recurve storms can impact Bermuda, and may also survive into the Canadian Maritimes.

Recent Example: Sam

- In 2021, Hurricane Sam reached Category 4 intensity in the central Atlantic Ocean.

- However, a jet-stream trough along the East Coast and a weaker Bermuda-Azores high curled Sam to the north, then northeast, far from any land concerns.

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. Extreme and bizarre weather are his favorite topics. Reach out to him on Bluesky, X (formerly Twitter) and Facebook.