The North Atlantic storm season has significantly ramped up recently, with 12 named systems. The current one, Storm Lee, is forecast to become the most intense system of the year. Taking advantage of the North Atlantic’s extremely warm sea temperatures, Lee is expected to rapidly intensify and likely reach a Category 5 over the weekend. On its way towards the Bahamas and the United States.
This year, the record-high average sea surface temperature resulted in intense storms; two Category 4 systems have already been observed, Franklin and, most recently, Idalia. The next, Lee, will surpass them and become the first Category 5 storm of the Atlantic season in 2023.
Lee is forecast to track to the north of the Leeward Islands towards the Bahamas and the United States. Still, the exact track is to be determined as the main rapid intensification is yet to arrive in the following days.
This high activity comes after months of unusually high water temperatures in the Atlantic Basin region.
Note that warmer sea waters lead to the highest potential for more tropical systems, including their intensity, during the Atlantic Storm Season, which lasts from June through November. Additionally, given the warm waters, the chances for tropical storms reaching the European continent are also higher than usual this year.
THE HOTTEST-THAN-EVER AVERAGE TEMPERATURE MEASURED OVER THE NORTH ATLANTIC BASIN
Temperatures at the North Atlantic Ocean surface temperature reached the highest-ever levels in the history of measurements. At the end of July, the daily average temperature of the whole Atlantic Basin was an astonishing 24.9 degrees Celsius (76.8 °F).
Ocean water temperatures are still extremely high, from 30 to 32 °C across the western Atlantic Basin.
What was more shocking than the record value was that the North Atlantic usually reaches its highest temperatures in early September, two months before the usual peak values.
With the statistical data, the sea surface temperature in the Atlantic Ocean is generally higher late in the summer. It continues to rise in August towards its usual highest values observed in mid-September every year. The previous record was set last year, in September 2022.
These so-called marine heatwaves are becoming more frequent and intense in recent years. This year, they are more persistent and spread over large areas. The 24.9 °C mark in July was more than one degree warmer than a 30-year climatological normal, calculated from 1982 to 2011.
The tropical central and western Atlantic regions remain well above normal as we were in the final month of meteorological summer 2023. This correlates well with what is typically seen before active Atlantic storm season. The near-term SST anomaly forecast also hints temperatures will continue to rise in the main storm development region.
We expect that these sea waters of the North Atlantic will be sufficiently warm enough to support significant tropical development during the peak of the storm season from September into October.
During the summer months, we closely monitor Western Africa’s weather conditions. This is where the tropical waves emerge into the eastern Atlantic Ocean. Data shows that nearly 85% of these waves lead to organized deep convection over the warmer oceans, become depressions, and later get upgraded into storms.
ATLANTIC STORM SEASON 2023 FORECAST
The 2023 Atlantic storm season has started on June 1st. After mid-August, the activity normally starts increasing, toward the peak in September and October.
There were already two Category 4 and one Category 1, making the count of 13 storms in 2023. This year, the ongoing strong El Nino effect is forecast to bring lesser activity due to stronger wind shear in the tropical region.
However, the unusually warm and hottest-than-ever sea waters of the North Atlantic could increase activity, mainly in terms of the more rapid strengthening of the cyclones and their peak intensity. Research studies have found that the warmer the waters are, the higher the potential for more intense systems.
The seasonal forecasts from the Colorado State University (CSU), led by Dr. Phil Klotzbach, hint at 18 named tropical systems, with nine Category 1+ and four major storms forecast for the Atlantic storm season 2023. That’s well above the 30-year average. Based on the long-term average, one season normally brings 14 named storms, seven of Category 1 or higher, where three reach a major intensity (Category 3 or greater).
Judging by these outlooks, the Atlantic storm season 2023 could be stronger than the one we had last year. To keep things on track, the 2022 season produced 16 total systems, where 14 of those were storms, and 8 were Category 1 or higher. Those major storms were Fiona (Category 4) and Ian (Category 5), both occurred in September 2022.
This is a NOAA visible satellite view of Category 5 storm Ian in the final days of September when it was nearing the southwest Florida peninsula.
The Atlantic season runs from June 1st through November 30th. The region we monitor these storms is known as the Atlantic basin, which covers the tropical area, including the entire Atlantic Ocean, the Gulf of Mexico, and the Caribbean region.
The long-term average of tropical systems in the Atlantic Basin (taken over the last 70 years – between 1951 and 2020) holds 11 named storms in one full season. However, the short-term average (taken over the last 15 years – between 1995 and 2020) is higher, with around 14 named storms. We can notice a gradual increase in the number of storms.
While a La Nina global weather pattern influenced the last three seasons, the 2023 Atlantic storm season will have an El Nino effect. Which NOAA forecasts to peak in the fall months. El Nino is known to lead to lesser tropical activity due to stronger wind shear in the Atlantic Basin.
However, despite El Nino throughout the year and this year’s well-above-average Atlantic seawater temperatures, the upcoming peak season is again expected to be busy. These warmer-than-normal sea temperatures are also observed across the Caribbean and the Gulf of Mexico.
The Atlantic, the Caribbean, and the Gulf are warmer than normal, including across the region known as MDR (the Main Development Region – between Africa and the Caribbean Sea). This indicates that upcoming cyclone formation will fuel from the warm and hottest-than-ever ocean waters.
A tropical storm organizes and gains its strength when specific weather conditions are met. Normally, we need a low-shear environment with very warm sea waters. The latter results in plenty of very moist air mass above the sea.
ATLANTIC STORM SEASON 2023 ALREADY HAD 13 EVENTS SO FAR
The WMO’s international committee (the World Meteorological Organization) has designated 21 storm names for the Atlantic season 2023. The list with all the cyclone names can be seen below, starting with Arlene and ending with Whitney.
So far, thirteen systems have formed in the first four months of this storm season. There was one Category 1 storm (Don) and two Category 4 storms, Franklin and Idalia. Before the official start, there was one sub-tropical storm in January.
We use cyclones’ names for one main reason – to help quickly identify storms in warning messages.
LEE EXPECTED TO TAKE RAPID INTENSIFICATION TOWARD A CATEGORY 5 STORM
The recent geostationary satellite imagery shows that the convective structure of Lee has improved. The system is moving west-northwestward at about 12 kt to the south side of a low- to mid-level ridge over the central Atlantic.
The track guidance suggests that the core of Lee will pass to the north of the northern Leeward Islands.
On Thursday, the well-organized low-level structure of the cyclone will lead to rapid strengthening as Lee travels across warm Atlantic seawaters of 29-30 °C during the next few days.
The NHC intensity forecast brings Lee to a major storm (Category 3 or greater) within 48 hours. It will likely continue strengthening on Saturday and reach a violent Category 5 strength over the weekend.
Due to eyewall replacement cycles, some fluctuations in intensity later in the weekend and early next week are expected.
Lee is forecast to become a major storm by early Saturday and a Category 5 around Sunday or Monday. It could impact the northern Leeward Islands this weekend before continuing west-northwest towards the Bahamas and the U.S. early next week.
The following chart represents Lee’s peak wind gusts swath over the next ten days. It becomes a violent storm as it tracks toward the west-northwest in a few days. Peak gusts when it approaches the Bahamas, could exceed 185 mph.
Lee will likely change its direction and track more toward the northwest after Sunday so that the exact future path will be closely monitored. The eastern U.S. Atlantic coast needs to have close eyes on the storm.
The rainfall accumulation map also indicates the projected violent storm Lee; this weather model finds around 30″ of rain as the peak.
RECORD-WARM ATLANTIC COULD BOOST FUTURE STORMS AND THEIR INTENSITY
As we discussed earlier above, the extremely high water temperatures across the Atlantic, including the Main Development Region, have something that has never been observed before. This means that one of the main conditions that fuel tropical cyclones is particularly anomalous – the heat content.
For a tropical storm to form, two meteorological features must be present:
- A weather disturbance, such as a cluster of thunderstorms that pulls in warm surface air (dewpoints) from all directions
- The water at the ocean’s surface has to be at least 79° Fahrenheit (26° Celsius)
Because of the interaction of warm air and seawater that spawns these storms, these cyclones form over the oceans between about 5 and 20 degrees of latitude. At these latitudes, seawater is warm enough to give the storms strength and the rotation of the Earth, which makes them spin.
So, in general, these systems start with the evaporation of warm seawater, which pumps water into the lower atmosphere. This significantly humid air mass is dragged aloft when converging winds collide and turn upwards.
As air rises to higher altitudes, water vapor condenses into clouds and rain, releasing heat. This warms the surrounding air, causing it to rise with the air far above the sea moving upward; even warmer, moist air spirals in from along the surface to replace it.
Therefore, as long as the base of this weather system remains over warm water and high-altitude winds do not shear apart its top, the cyclone will be strengthening and growing. More and more heat and water will be pumped into the air.
The surface central pressure at its core will drop further, sucking in the wind at ever-increasing speeds. Over several hours to days, the tropical storm (cyclone) will intensify, finally reaching greater strength. A cyclonic system in the North Atlantic officially gets a Category 1 status when the winds that swirl around it reach sustained speeds of 74 miles per hour (64 knots or 119 km/h) or more.
Warmer oceans provide more potential energy for these systems, leading to stronger storms or even more rapid intensification when they grow. Recent studies have shown a link between ocean surface temperatures and tropical storm intensity – The warmer waters lead to more intense storms.
So, as we learned, the two main ingredients tropical systems need for their formation and strengthening are (1) a weather disturbance and (2) warm ocean waters. The latter has been in the record values for the whole North Atlantic.
Seawaters remain extremely warm throughout summer and generally peak in September, the most active period of the Atlantic Season. This increases the chance that the upcoming tropical systems will take advantage of these conditions and support explosive and rapidly developing storms.
SAFETY PREPAREDNESS FOR THE STORM SEASON
Have a plan
The main storm season in the North Atlantic and the Caribbean starts on June 1st and ends on November 30th. This is when you and your family must be prepared by planning.
- Write emergency phone numbers and keep them on the refrigerator or near every phone in your house. Program them into your cell phone as well.
- Prepare an emergency supply kit.
- Locate the nearest shelter in your area and different routes from your home in an emergency. If shelter locations in your area have yet to be identified, learn how to find them before the event of a storm.
- Pet owners: Take care of your pets at pre-identify shelters, a pet-friendly hotel, or an out-of-town friend or relative where you can take your pets in case of an evacuation. Local animal shelters can offer advice on what to do with your pets if you are asked to evacuate your home during a storm.
LEARN THE DIFFERENCE BETWEEN A “WATCH” AND “WARNING”
When you listen to the National Weather Service alerts on TV or radio or check for them online, there are two kinds of alerts:
- A watch means severe conditions (sustained winds of 74 miles per hour [mph] or higher) are possible in a stated area. The NH) will announce watches 48 hours before they expect tropical-storm-force winds (sustained winds of 39 to 73 mph) to start.
- A warning is a more serious threat to deal with. It means violent winds are expected in a stated area. NHC issued these warnings 36 hours before tropical storm-force winds were expected in the area to give people enough time to prepare for the storm.
Check out the NHC for more information about watches and warnings. If you hear a watch or warning in your area, you can take steps to get ready.
GET YOUR CAR READY TO LEAVE HOME IF NEEDED
Make sure your car is ready before the tropical storm hits.
- Fill the gas in your car’s tank.
- Move cars and trucks into your garage or under cover.
- Always keep an emergency kit in your car.
If you don’t own a car, consider making plans with friends and family or call authorities to get a ride if you need to evacuate.
GET YOUR FAMILY AND PETS READY
- Go over your emergency plan with your family; understand everything.
- Keep checking for weather updates about the storm. Watch TV, listen to the radio, or check the NHC website online.
- Call the hospital, public health department, or the police about special needs. If you or a loved one is older or disabled and won’t be able to leave quickly, get their advice on what to do.
- Put pets and farm animals in a safe place.
GET YOUR HOME READY
- Clear your yard to ensure nothing could blow around during the storm and damage your home. Move bikes, lawn furniture, grills, propane tanks, and building materials inside or under the shelter.
- Cover up house windows and doors. Use storm shutters or nail pieces of plywood to the outside window frames to protect your windows. This can help keep you safe from flying debris and pieces of shattered glass.
- Be ready to turn off your power if you see flooding, downed power lines, or you have to leave your home. Switch your power off completely.
- Fill clean water containers with drinking water if you lose your water supply during the storm. You can also fill up your sinks and bathtubs with water for washing.
- Double-check your carbon monoxide (CO) detector’s battery to prevent CO poisoning.
BE READY TO EVACUATE OR STAY AT HOME
During a warning, always listen to authorities regarding whether you should evacuate or stay home.
If a storm is coming, you may hear an order from authorities to evacuate (leave your home). Never ignore an order to evacuate. Sturdy, well-built houses may not hold up against a storm’s power. Staying home to protect your property is not worth risking your family’s health and safety.
There are occasions when you may hear an order to stay at home. If driving conditions are too dangerous, staying home might be safer than leaving. Respect the authorities’ decisions.
If you need to evacuate:
- Grab your emergency supply kit and only take what you need (cell phone, chargers, medicines, identification like a passport or license, and cash).
- Unplug your appliances. If you have enough time, turn off the gas, electricity, and water.
- Follow the roads that emergency workers recommend even if there’s dense traffic expected. Other routes might be blocked or already flooded. Never drive through flooded areas, as cars and other vehicles can be swept away or may stall in just 6 inches of moving water.
- Contact your local emergency management office and ask if they offer accommodations for owners and pets.
If you need to stay home:
- Keep your emergency supply kit anywhere where you can easily access it anytime.
- Follow weather updates online from NHC, and listen to the radio or TV for updates on the storm.
- Stay inside. Even if it looks calm, don’t go outside. Wait until you hear an official message that the storm is over. Sometimes, the weather gets calm in the middle of a storm but then quickly worsens again.
- Stay away from windows — you could get hurt by flying debris, such as pieces of broken glass or other objects winds pick up around the neighborhood during the storm. Stay in a room with no windows, or go inside a closet.
- Be ready to leave home. If emergency authorities order you to leave or your home is severely damaged, you may need to go to a shelter or a neighbor’s house.
Our expert forecaster team will actively follow the tropical region activity worldwide, including Atlantic Basin systems and tropical cyclones likely to affect the United States, the Caribbean, and Europe again in the following months.
Stay tuned for further follow-up posts, in-depth forecast discussions, and nowcasting during the coming weeks and the upcoming Atlantic storm season 2023 peak weeks. We will make you prepared.
Copernicus, NOAA, NHC, Colorado State University, Tropical Tidbits, and WHO provided images used in this article.
We thank our partner, ClimateBook, for providing high-quality featured graphics in this article.
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