#alas the pretty satellite image is near the bottom so you'll have to scroll to find it

[mxanigel]

Hey Ani! If I remember correctly, you’re hella knowledgeable about weather, right? If I am remembering that correctly, can I ask you a question about something?

(I’ve heard the Bering Sea has a lot of “hurricane force winds”. How can you have those conditions but not a “hurricane” (is there a cold water equivalent?) even when there’s a storm?)

If I’m mistaking you for someone else, I am. So sorry 😅 please ignore me.

But if you are, and you’re up for answering, I’m so intrigued 🖤

Either way, hope you’re doing well 🖤

AAAAAH this ask made me flail and geek out, thank youuuu~ also, this is a fantastic question. *cracks knuckles* Brace yourself for a very happy scientist's ramblings!

Hokay, so the atmosphere would prefer to be in balance. But land heats up/cools down faster than water, places closer to the equator (low latitudes) tend to be warmer than places farther away (high latitudes), and some places are super dry (like deserts) while others are really moist (like rainforests). Temperature and moisture differences such as these affect atmospheric pressure, and pressure imbalances produce winds because air moves toward low pressure and away from high pressure, though not necessarily directly from one to the other due to other factors like friction.

Hurricanes are low-pressure systems that form over tropical oceans and are "powered" by thunderstorms (which are also known as "deep convection" because they're made up of very tall convective clouds, a.k.a. thunderstorms). Those clouds get their energy from warm ocean water and help form the low pressure around which the winds spin. The Saffir-Simpson hurricane wind scale (SSHWS) is the scale by which we categorize hurricanes, specifically by their maximum surface winds averaged over a 1-minute period. (Such winds tend to be highest over the ocean; for example, a landfalling category 1 hurricane may never produce hurricane-force winds over land due to increased friction from the land slowing down the winds. But that's a ramble for another time.)

Generally speaking, a hurricane is a type of "tropical cyclone." When a tropical cyclone in the North Atlantic or eastern North Pacific has maximum winds of 39-73 mph, it's a tropical storm, and reaching a maximum wind of 74+ mph makes it a hurricane. This means 74 mph is the hurricane-force wind threshold.

Extratropical storms are also low-pressure systems, but instead of forming over warm ocean water and being powered by thunderstorms, they result from the collision of warm and cold air masses at higher latitudes (hence the term "extratropical" meaning "beyond the tropics"). The warm air masses often come from the tropics, which makes them juicy too (that is, they carry a lot of moisture with them). The cold air masses tend to be drier, increasing the contrast between the two. Since continents are often the source of the cold + dry air, extratropical storms can develop over ocean or over land!

Strong extratropical storms can produce surface winds that exceed 74 mph, which earns them the moniker "hurricane-force low" because that's the SSHWS threshold for a hurricane. On a weather map, they'll get a label when they reach this intensity, like this storm south of Alaska in early October 2021:

Visible satellite image source (NASA Worldview) Surface analysis map is from the Ocean Prediction Center

For more information, this ArcGIS StoryMap from the Ocean Prediction Center nicely discusses hurricane-force lows that occurred during Spring 2021-Spring 2022 in the Northern Hemisphere.

I hope this ramble clarified a bit about these storms! Thanks again for sending the ask -- I loved diving into the answer.