Under the Weather: Another hurricane poised to strike the Gulf Coast while the rain train returns to the Pacific Northwest

The 2020 Atlantic hurricane season is on pace to be a record-breaking one, with the potential of outdoing 2005, a year featuring infamous storms such as Rita, Wilma, and Katrina. We have already blown through all 21 names in the name list and had to begin using the Greek alphabet—a feat only done in 2005 thus far.

A tropical cyclone, a general term for these storms, gets named when it reaches tropical storm status, with sustained wind speeds of at least 39 mph. It is designated a hurricane when/if it reaches 74 mph, and then rated on a 5-category rating system called the Saffir-Simpson scale, based on wind speeds.

By Oct. 5, 2005, 20 storms had been named (including tropical storms and hurricanes). As of the same day in 2020, we are at 25 named storms—and there is still plenty of time left in the season. It is quite possible that we will exceed the record-setting 28 named storms set in 2005.

The latest tropical threat to the United States is Hurricane Delta, which has already made landfall near Puerto Morales, Mexico (just south of Cancun) as a category 2 hurricane, with wind speeds of 110 mph. However, it has since emerged in the Gulf of Mexico, and is now poised to strike areas already impacted by tropical systems earlier in the season, particularly Hurricane Laura at the end of August.

The latest forecast cone for Hurricane Delta is shown below. This indicates the area where the center of the storm could go, though impacts could be felt outside of this cone. The cone is determined through ensemble runs showing possible paths of the storm center (i.e. the eye). Currently, it is a 120-mph category 3 hurricane. It is expected to make landfall sometime Friday evening, but the intensity at landfall is uncertain. It is possible that it weakens some before landfall due to cooler sea surface temperatures right along the coast, but significant impacts—such as high winds, storm surge, and heavy rain—are still expected regardless.

Thankfully, here in the Pacific Northwest, we do not have to contend with tropical systems like hurricanes and tropical storms. To understand why, it is important to know that these storms are fueled by warm ocean waters, primarily above about 27°C (equivalent to about 80°F). All these storms form over open waters, in areas with very warm ocean temperatures. Oftentimes, the most powerful tropical systems form over the warmest waters (although there are other factors, as well). Once these storms pass over land, their energy source is cut off, and they begin to weaken.

Look at a map of the sea surface temperatures around the United States, via NOAA:

Notice the areas of extremely warm waters in the areas with oranges and reds (also note that the temperature scale is in Celsius, not Fahrenheit). Now also look at the graphic below (found here, showing all the origin points and tracks for tropical systems for the first ten days of October. Almost all these occurred in the areas with very warm waters.

Looking at the areas surrounding the Pacific Northwest, the sea surface temperatures are much colder, and not surprisingly, there have been no tropical systems even remotely close to us. Occasionally, remnants of tropical systems can make it to our area, but that is after they undergo an extratropical transition, turning from a tropical cyclone into a midlatitude cyclone.

Midlatitude cyclones are much larger than their tropical cousins and are formed through different processes and dynamics. These storms are common for our area during the fall and winter. So, while we don’t get tropical cyclones, we get midlatitude ones (I will dive a bit more into mid-latitude cyclones in a future article).

Now a look at your forecast:

Apart from a few rain events during the first few days of fall, the weather has been relatively calm. But things are about to get going with a few systems heading our way, starting this weekend.

Take a look at the GFS ensemble showing 24-hour precipitation totals for Paine Field. All the ensemble members are showing a wet week ahead. The first system arrives late Friday into Saturday, bringing with it a decent amount of rain, as well as gusty condtions. After this system passes, unstable conditions will likely follow, meaning there is the chance of some isolated thunderstorms through Saturday night. Sunday isn’t looking quite as wet, but still should see scattered showers throughout the day. A couple other systems are expected to follow next week, though at this time, they are not looking as robust as the first one. After this, there is the chance for another rain break by the end of next week, but I’ll be keeping an eye on things as we get closer. By this time next week, we could have accumulated between 2 and 3 inches over the area. Depending on if/where heavier showers and thunderstorms form, this total could be higher. I don’t know about everyone else, but I’m so ready for this stormy weather!


— By Kelsie Knowles

Kelsie Knowles is a meteorologist and recent University of Washington graduate who lives in north Lynnwood. After writing weather blogs as a KOMO News intern, she discovered a passion for writing about weather. You can learn more in her blog www.wxnoggin.com and you can also follow her on Twitter at @kels_wx3.




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