It's that time of year: the 2024 Atlantic hurricane season begins today! It's time to start the preparation process if you haven't already. We can be thankful that we escaped the preseason period with no named storms; it's only the second time in the last ten years that this has been the case.
As we begin today, we have no features showing signs of further development, but there are a few tropical waves to track out there. One is near 78° west longitude, another near 53° west, and a third hidden in the Intertropical Convergence Zone near 35° west.
A loop of visible satellite images from this morning shows quiet weather across the tropical Atlantic with only a few tropical waves to track.
Image source: University of Wisconsin RealEarth
This time of year, the primary areas to watch for development are the Gulf of Mexico, the far southwestern Atlantic, and the western Caribbean Sea. So, it's no surprise that the western Caribbean will be an area that we need to watch over the next couple of weeks. Computer models indicate that we will see disturbed weather in this area as cold fronts get unusually far to the south and the first few tropical waves of the season pile into the area. There is a chance that we see a development come out of this setup. Elsewhere, westerly winds aloft or a dry and stable atmosphere will prevent storms from forming despite ocean temperatures running well above average for early June. Currently, computer models show either no development or a weak system moving northeastward out of the Caribbean Sea, over the islands, and away from us over the Atlantic.
So, for now, we don't have any imminent threats to South Carolina, and it doesn't look like we'll have to deal with one during the first part of June. However, this season looks active, so our chances are higher than usual of being affected by a tropical cyclone at some point during the season.
Over the last 50 years, South Carolina has had an impact (either a landfalling storm or a nearby storm causing significant effects in the state) from a tropical cyclone in 43 years, corresponding to an 86 percent chance of seeing an impact each year. For hurricanes, the return interval is about one every eight years, corresponding to about a 13 percent to see one each year. For major hurricanes, the return interval has been about one every 34 years.
Now seems like a good time to point out that our last major hurricane was Hugo, just under 35 years ago. That doesn't necessarily mean that we're due for another storm that strong; it may be another 35 years before we see another one (I hope so; I'll be retired by then). On the other hand, this could be the year. The historical return interval equates to about a 3 percent annual chance for us to see a major hurricane in South Carolina, and we have to roll that d100 every year whether we like it or not.
So, armed with some climatological information, let's delve into the outlook for this year. Several public and private sector entities in the United States and abroad issue seasonal hurricane forecasts. You can find a more complete group of them at a website operated by the Barcelona Supercomputing Center called seasonalhurricanepredictions.
There is a strong consensus that the upcoming hurricane season will be active to hyperactive with more storms than we saw last year. Last year, there was an above-average number of named storms but a near-average number of hurricanes and major hurricanes. The best-known entity for hurricane season forecasts is Colorado State University because they have been doing these seasonal forecasts since the 1980s. NOAA is the parent federal agency of the National Weather Service, so they are well-known experts in the field. The other four entities in the chart above are private-sector companies.
These forecasts strictly apply to the number of storms that will occur this year and do not attempt to forecast where the storms will go and how many will make landfall in South Carolina or elsewhere in the basin. I know of one exception: WeatherBELL includes a forecast of areas with a higher risk of landfall with their subscription service.
When I compiled my outlook months ago at the request of another state agency, I attempted to quantify the chances of South Carolina feeling a hurricane impact this season. By hurricane impact, I mean either a landfall in the state or a nearby hurricane causing at least 74 mph sustained winds at some point in the state. I base my estimate of a 20 percent chance for a South Carolina impact on how much more active than normal this season will be, comparing that to the roughly 13 percent chance we have of a hurricane impact each year.
By the way, this Accumulated Cyclone Energy thing measures how much energy a tropical cyclone expends during its lifetime, and the figures in the chart above are a sum of all the storms in a season.
There are several reasons why there is a consensus that this hurricane season will be active; two reasons stand out. First, ocean temperatures across the North Atlantic Basin's Main Development Region (the part between 10° and 20° north latitude) are much warmer than average, as is most of the rest of the basin. As you likely already know, warm waters are hurricane fuel, so having the waters out there much warmer than usual should result in more storms and stronger storms this season.
A plot of sea surface temperature anomalies over the Atlantic Basin, indicating warmer than usual waters over most of the North Atlantic.
Source: WeatherBELL
The other is the current state of ENSO, El Niño - Southern Oscillation. ENSO is the combination of El Niño (when waters in the equatorial East Pacific are warmer than average), La Niña (when waters in the equatorial East Pacific are cooler than average), the neutral phase (when waters in the equatorial East Pacific have a near-average temperature), and the impact these water temperature changes have on the atmosphere. Last season, an El Niño was occurring, which limited Atlantic tropical cyclone activity by causing more vertical wind shear over the Atlantic. The El Niño is fading now, and La Niña is coming on strong. La Niña conditions in the East Pacific favor more Atlantic tropical cyclone activity because wind shear is less.
The effects of El Niño and La Niña on Atlantic tropical cyclone activity.
Image source: NOAA
So, we have two major factors indicating the potential for a very active hurricane season. Other factors, such as comparisons to past seasons with similar preseason conditions, computer forecasts, and the direction and strength of cross-equatorial flow in the Atlantic (the Atlantic Meridional Mode, which you can google if you dare) are more things that forecasters consider, and all of them point toward an active hurricane season this year.
The bottom line is that we expect a busy hurricane season in the Atlantic. While we don't have a good feel about where most of the storms will track, we are concerned about the number of storms we expect to see this year. Having more storms increases our odds of being hit by at least one of them. Does that mean you should prepare harder this year? Well, you should prepare hard every year because even the quieter seasons usually have one major hurricane. For example, 1989 was a near-average season in terms of overall activity for that time, with 11 named storms, seven hurricanes, and two major hurricanes, but one of those hurricanes was Hugo. The people of South Florida will tell you all about Andrew, a Category 5 hurricane that hit them in the otherwise mundane 1992 hurricane season.
So, prepare hard each season. Besides, hurricane preparation is generally good all-hazards preparation, and we face plenty of hazards here in the Palmetto State between the weather and our state's seismology. I urge you to spend some time at SCEMD's hurricane.sc website, where you'll find preparation advice for you and your family (including the furbabies).
