The first two months of hurricane season have been one of the quietest in recent memory. Only three storms have been named so far, and one of them was actually over land. This has come as a bit of a surprise to people both inside outside of the weather community since forecasts for the 2022 season called for above-average activity with up to 20 named storms. However, it is my opinion that the peak of this hurricane season will be very active, so I want to explain why I think so and why some experts are coming to the same conclusion.
It’s best to start out by looking at the expected trends of any hurricane season to help us get an idea of how active the tropics should be. The chart below shows the number of tropical storms and hurricanes by date, collected from hurricane seasons 1944-2020. The peak of activity falls on September 10. I think one of the most important takeaways from this image is that only 10% of all hurricanes form before August, so a slow start to hurricane season doesn’t have much of an impact on what the rest of the season may look like.
Besides the climatology above, one of the reasons why we should start seeing more tropical activity soon has to do with something called the Madden-Julian Oscillation (MJO). It may not be as well-known as other weather patterns like El Nino or La Nina, but the MJO plays a big role in tropical patterns each year (plus winter patterns as well). Think of the MJO like a “pulse” of moisture that slowly moves eastward along the Equator, slowly moving around the entire planet every 30-60 days before arriving at its initial point and repeating the same pattern again. When this “pulse” reaches a certain location, it can make Atlantic tropical activity much more favorable. On the contrary, it can help suppress activity when in other locations. The takeaway here is that the MJO can be responsible for active and inactive periods within a single hurricane season.
Back in late June 2022 the MJO was in a (relatively speaking) favorable location for the Atlantic. I say relatively speaking because June is still very early in hurricane season, so even with the MJO’s help, you wouldn’t expect to see a lot of tropical activity. However, an infrared satellite image at that time really caught my attention. In an area of the tropics known as the “Main Development Region” which is a common area to the west of Africa for tropical systems to form in late August and September, there were already four distinct clusters of tropical thunderstorms. I thought it was very unusual for that area to be so active so early in the season, which makes me think if the MJO becomes favorable again during the peak of hurricane season (which it is currently forecast to do), then that will make the Main Development Region even more likely than usual to spawn tropical storms and hurricanes.
Aside from the MJO, another method meteorologists have for seasonal forecast is the use of analogs. I’ve written in the past about using analogs for winter forecasting, but they can apply to tropical forecasts too. Analog forecasting is basically a way of comparing past weather conditions to current weather conditions and using that to create a more accurate forecast. It was noted last week that ocean temperatures around the globe this summer look very similar to ocean temperatures from 1950.
While most people (understandably) wouldn’t care about ocean temperatures from 72 years ago, they’re important in this case because of how the 1950 hurricane season played out. The graph below shows how the 1950 hurricane season evolved month-by-month, how long each storm lasted, and how intense each storm became. It begins in August since there were no named storms beforehand. All of a sudden there were six hurricanes (four major hurricanes) in just four weeks! Just another example of how this hurricane season has “light switch” potential to go from almost nothing to highly active very quickly.
Before the beginning of every hurricane season, seasonal forecasts are issued by NOAA and Colorado State University, which are two of the best institutions for hurricane predictions. CSU’s forecast was for 20 named storms, 10 hurricanes and 5 major hurricanes – definitely a busier season than usual. NOAA’s forecast was about the same. Both places issued an update this past week, and despite the very quiet start to the hurricane season so far, the seasonal forecasts have barely changed. That alone makes me think we’re in for a lot of tropical activity in a short period of time, but when reading some of NOAA’s discussion, it makes physical sense too.
One of the main reasons NOAA thinks we’re still due for a busy season is because of La Nina conditions staying present through the summer and into the fall. La Nina is responsible for weak wind shear in the Atlantic Ocean. If wind shear is weak, that means tropical systems can grow in a more organized structure and potentially develop an eye. The left side of the image below shows that kind of scenario, while the right side shows what happens when wind shear is strong – the thunderstorms get “ripped apart” by the wind differences and any tropical system will have a ragged and unorganized appearance on satellite. The weak wind shear from La Nina will make it more likely that tropical systems maintain their strength as they head across the Atlantic Ocean.
Now that you know why 2022 is still likely to be a busy hurricane season, it’s important to remember that no matter where you are along the coast, it only takes one storm to potentially cause life-changing damage. It’s always a good idea to be prepared ahead of time.
WeatherBolt 