• Bryan Norcross

Surprise Tropical Storm Colin forms on the Carolina coast while Bonnie crosses Central America

In a surprise, the small low-pressure system off the coast of South Carolina met the requirements to be called Tropical Storm Colin overnight. It’s not uncommon for very small systems to spin up quickly over the warm and deep Gulf Stream waters off the Carolinas. A similar thing happened in 2020 with Tropical Storm Bertha.


A system needs to stay organized for nominally 18 hours to meet the definition of a tropical storm, which Colin did. And therefore, it was named this morning.


The biggest effect from Colin will be in eastern North Carolina. Winds could gust to 30-35 mph in squalls that rotate in off the ocean through today and tonight. Colin should be past the area tomorrow and is expected to merge with a cold front and die offshore by Monday.



The disturbance that became Colin began as a non-tropical area of low pressure near the Bahamas last Monday. As it moved north, it was forecast to track far enough inland, that it was not given much thought. In the end, it spent enough time over the Gulf Stream just off South Carolina to get enough energy to spin up into a tropical system. Its track to the north is now over the land, but just close enough to the coast to maintain a circulation.


The upper-level winds are making the storm lopsided, which kept most of the bad weather offshore of the South Carolina coast. Squalls are rotating into North Carolina, however.


The surprise here is not that stormy weather is affecting North Carolina, but that it’s being caused by a tropical storm, which will likely make some of the downpours a bit more gusty.



Over Central America, Tropical Storm Bonnie is crossing Nicaragua on its way to the Pacific Ocean.


Since Bonnie is maintaining its circulation, it will still be called Bonnie over the Pacific. This is only the second time since the naming rules were changed in 2000 that this has happened – the first being Otto in 2016. Previously all systems that reached the Pacific got new Pacific names.


Most often, systems that cross Central America get ripped apart by tall mountains, but Bonnie and Otto found a relatively narrow piece of land with less elevation. If the circulation stays intact, the new rules say the name is kept.


Bonnie is forecast to track to the north offshore of Central America and Mexico, but not far from the coast. They will have to watch it carefully.


The Tropical Disturbance over the eastern Caribbean is unlikely to develop. It will bring some heavy rain and gusty winds to the islands, however, as it spreads west across the Caribbean Sea.


Elsewhere, nothing appears to be pending through the middle of next week at least.