Fifth Named Storm of the Season Ernesto
Ernesto became the fifth named storm of the Atlantic hurricane season yesterday, forming just ten days ahead of the climatological average for the fifth storm. This might seem surprising given the aggressive seasonal forecast predicting a hyperactive season with 23 named storms.
This morning, Ernesto passed over the island of Guadeloupe at 5 a.m. Tropical storm warnings are in place across the northern Leeward Islands, the Virgin Islands, and Puerto Rico, and tropical storm conditions are expected to continue in the coming 24 hours across the region.
As Ernesto crosses Leeward Island, the insurance industry must wonder why Ernesto has not exploded into a major hurricane like Beryl did as it approached the southern Caribbean islands. After all, the ocean heat content is high, with near-record warm Sea Surface Temperatures (SST). However, ideal conditions are necessary for tropical cyclone development and intensification, and Ernesto is currently facing a challenging atmospheric environment. Unlike Beryl, Ernesto is a large tropical wave, which makes cyclogenesis (spin) more difficult to organize. Additionally, the presence of dry air and Saharan dust further hinders storm formation. Another notable factor is Ernesto's unusually fast movement. When the storm was named yesterday, Ernesto was moving at a fast 28 mph. According to Michael Lowry, a hurricane expert at WPLG in Miami, less than 1% of all estimates of forward speed for named storms occurring in the deep tropics (south of 20°N) have been as fast as Tropical Storm Ernesto during the satellite era (since 1966). This fast motion also contributes to the difficulty for cyclogenesis to occur.
Ernesto has recently slowed to a more manageable 18 mph, allowing the storm to gradually strengthen and become better organized. The forecast is relatively clear, with track models consistently predicting the storm will turn right over and north of Puerto Rico late today or early tomorrow. The Virgin Islands and Puerto Rico are expected to experience gusts of 50 to 60 mph. Given Puerto Rico's recent issues with its power grid, as seen with Hurricane Fiona in 2022 which resulted in a black out across the island, there's concern about potential power outages. Additionally, even a passing tropical storm can cause significant impacts, such as flash flooding and mudslides, due to heavy rain bands accompanying Ernesto.
After heading past Puerto Rico, Ernesto will head north over the open sea with very warm sea surface temperatures. At this point, the turn north is good news for the insurance industry and a U.S. landfall is unlikely, with only Cape Cod having less than a 5% chance of seeing tropical storm-force winds. As Ernesto turns north, it will slow down and encounter favourable conditions with less wind shear and warm sea surface temperatures. It is predicted to become a hurricane by Thursday or Friday. The forecast is for Ernesto to slow down very close to Bermuda as at least a Category 1 hurricane. Still, there is some forecast support for a Category 2, potentially a Category 3 hurricane. At this point, Ernesto will likely be considered what meteorologists call a fish storm. Nonetheless, we will need to monitor model tracks as it gets closer to Bermuda.
What is amazing is how the insurance hub of Bermuda can be in the crosshair of so many named storms, given its overall size (21 sq miles) in the large North Atlantic Ocean (16M sq miles). Bermuda is no stranger to storms, with nine storms near the island since 2020. Remember, just in 2020, Hurricane Paulette hit with 90 mph winds, and the eye passed directly over while turning N.E. Last hurricane season, Lee tracked just to the west of the island as a large hurricane. In fact, in its long history, Bermuda gets brushed by a named storm every 1.69 years and gets hit by a hurricane about every four years. It is too early to tell if the storm will progress west or east of the island or make an unlucky direct hit. Lastly, Atlantic Canada could see effects from post-tropical Ernesto. Therefore, between Bermuda's and Atlantic Canada's, the insurance industry cannot wholly discount Ernesto's impacts yet.
Looking Ahead
At the beginning of this update, we discussed that this season, in terms of named storm count, seems to match climatology. At the same time, Accumulated Cyclone Energy (ACE) is well above average due to the long-tracking powerful Hurricane Beryl earlier this season. A few tropical updates ago, we talked about how the spring is loaded and is going into the most active part of the Atlantic Hurricane season. We also discussed how this could be enhanced with the passing of a positive Madden Julian Oscillation. One might question the long-range forecast, which suggests minimal new named storm activity in the Atlantic basin through the end of August, with the possibility of only one more storm forming off the coast of Africa. This scenario could challenge the hyperactive seasonal forecasts. It is particularly intriguing given that just last week, Colorado State University updated its seasonal forecast and initiated its two-week outlook, both predicting a surge in upcoming activity.
If the long-range forecast is correct, the Atlantic Basin forecast for a hyperactive season will not verify if August is mediocre since July was inactive. The most active part of the Atlantic hurricane season is between August 20th through October 10th. The average number of named storms (tropical storms and hurricanes) that form in the Atlantic basin during this period is around seven to eight, while hurricanes that form during this period are around four to five. Major hurricanes are around 2 to 3. If we add a few more storms to the tail end of the season in October, we will get numbers that seem to point to more like 16 – 18 named storms this season, not 23.
The image above is the super-long-range ECMWF ensemble forecast (51 different forecasts) through September 10th, the peak of the Atlantic hurricane season. Besides the current Ernesto tracks, there is very little consensus on many new named storm activity for this forecast period. In this plot, stronger tropical storms will be green lines, and hurricanes will be blue and red tracks, which are few and far between, considering there are 51 different forecasts for the next 29 days.
In the meantime, keep a close eye on Ernesto. The season is likely to remain quiet until the start of September, aligning with climatological trends, as the peak of the season occurs around September 10th. Despite near-record warm water in the basin this season, other essential components for named storm formation are still needed. And so far, we have observed some negative climate factors affecting the season’s activity. The next named storm should form around August 28th and the forecasted steering flow needs to be watched as there could be a window for tropical trouble for the insurance industry yet.