Pro Meteorologist Explains the Hurricane Season // On The Wind Podcast #509

Professional delivery skipper Andy Schell sat down with meteorologist and weather-routing specialist Jeremy Davis on episode 509 of the On The Wind podcast to examine the dramatic divergence between the Atlantic and Pacific hurricane seasons.

Representing offshore training outfit 59° North Sailing, Schell questioned Davis on why the Atlantic had generated only 10% of its normal accumulated cyclone energy while the Eastern and Central Pacific endured record-breaking storm activity.

The Mechanics of Upper-Level Wind Shear and El Nino

The driving engine behind the inactive Atlantic season is a strengthening El Nino pattern across the Pacific Ocean. Under neutral or La Nina conditions, trade winds blow steadily from east to west across the tropical Pacific south of the equator, driving warm surface waters westward toward Indonesia and Australia. This regular circulation triggers deep ocean upwelling along the northern coast of South America and Peru, drawing cold, nutrient-dense water to the surface that can lower sea surface temperatures by 5 to 6 degrees Celsius below average.

During an El Nino pattern, those Pacific trade winds slacken or reverse direction. Warm equatorial water that normally pools in the western basin backtracks eastward, collecting off the coast of South America. The resulting expanse of warm ocean water fuels powerful updrafts of rising air across the eastern Pacific. Downstream across the equator and into the Atlantic basin, this convective displacement establishes an expansive upper-level trough.

That downstream trough generates punishing vertical wind shear throughout the tropical Atlantic, the Caribbean, and the Gulf of Mexico. While surface trade winds in the tropical Atlantic blow steadily from the east-northeast, mid-level and upper-level winds blow out of the west at 30, 40, and 50 knots. Davis explained the physical consequence of this speed and directional shear: “essentially tropical systems like to have not a lot of high winds aloft that can essentially like decapitate a system and tilt the circulation and rip it apart.”

Tropical Storm Dolly served as an instructive case study. Dolly formed west of Africa, tracked across the open Atlantic, and began to strengthen. However, as Dolly approached the Caribbean, fierce westerly winds aloft tore through the circulation, shredding the storm and preventing it from organizing into a hurricane.

Tropical Versus Extratropical Cyclones: Fronts and Latent Heat

Schell and Davis clarified the structural dividing line between tropical and extratropical low-pressure systems. An extratropical storm—such as a winter nor’easter in the northeastern US—derives energy from temperature contrasts between competing air masses. These systems feature cold, warm, and occluded frontal boundaries where cold air from the northwest collides with warm air from the southeast. In September, only about 1% of the extratropical systems that affect the northeast occur, making late-summer frontal storms an unusual event.

In contrast, a pure tropical cyclone has no frontal boundaries. It functions as a heat engine powered by latent heat release. As warm, moist air evaporates from sea surface temperatures of 25 to 26 Celsius or warmer, it ascends into the atmosphere, cools, and condenses. This condensation releases latent heat energy, lowering central surface pressure and sustaining the system. To survive, tropical systems require uniform warm, humid air, light winds aloft, and a position north of 10 degrees north for Coriolis spin. In contrast, dry air and atmospheric dust stabilize the atmosphere, preventing thunderstorm development and keeping systems at bay.

Cold fronts sweeping off eastern North America into the Gulf of Mexico or stalling near the Azores High can also initiate tropical cyclones. If a stalled front sits long enough, horizontal temperature contrasts wash out while leaving a localized disturbance. With warm water and low shear, that remnant can develop into a tropical cyclone. Tropical Storm Fay followed this path: it formed along an old front west of the Azores as a shallow system, steered southwest by low-level winds around the Azores High.

The ACE Index Split: 9.3 in the Atlantic Versus 254.4 in the Pacific

To measure storm strength beyond simple storm counts, meteorologists track the Accumulated Cyclone Energy (ACE) index. Calculated by squaring the sustained wind speed of an active system every 6 hours and dividing by 10,000, the index reflects accumulated kinetic energy. A weak 40-knot tropical storm adds little to the seasonal total, whereas a major Category 5 hurricane adds large values on an exponential curve.

Davis presented the statistical contrast between basins: “the ACE index right now is at 9.3 in the Atlantic. The climatology to date is 91.7.” At 9.3, the Atlantic stood at barely 10% of normal cyclone energy. Although the basin had recorded 8 named tropical storms, every system remained weak and short-lived. Not a single hurricane had formed. Davis noted that this marks the first time in the modern satellite era—which began in 1960—that the Atlantic reached this date without a hurricane. The last historical year to reach this point without a hurricane was 1914.

Meanwhile, the Eastern and Central Pacific generated extreme storm energy, reaching an ACE index of 254.4 compared to a normal of 110.1 to date—27 times the activity in the Atlantic. The Pacific produced 3 Category 5 hurricanes and 3 Category 4 hurricanes, subjecting Hawaii to two to three decades worth of tropical threats in one summer, with heavy orographic rains driving severe flooding.

Hurricane Polo reached Category 5 intensity three separate times, tying the Eastern Pacific record. Polo bottomed out at 892 millibars, the second-lowest surface pressure ever recorded in the Eastern Pacific. After crossing into the Gulf of California and moving into Mexico, Polo pushed heavy tropical moisture into Texas, New Mexico, Arizona, and Colorado.

The Risk of Mariner Complacency During Inactive Seasons

With offshore cruising boats heading south along the US East Coast and the ICW in November, Davis cautioned against letting down navigational vigilance: “Don’t get complacent. It’s you know you can have these outlier events that can happen.”

Historical data proves that quiet seasons can still produce destructive storms. Hurricane Andrew in August 1992 developed during an inactive season, yet made landfall as a catastrophic Category 5 hurricane in Homestead and South Florida before striking Louisiana as a Category 3 storm. Similarly, Tropical Storm Edouard formed in a brief window of favorable conditions in the Gulf of Mexico, flooding Texas; with another 24 or 36 hours over water, it would have become a hurricane. Localized pockets of low shear can emerge quickly in the Caribbean or Gulf during late autumn, supporting sudden tropical development.

Forensic Passage Debrief: 59 North Mapping and ECMWF ERA5 Telemetry

Connecting global climatology to offshore passage making, Schell shared an interactive mapping tool documenting 59 North’s 193,000 miles logged since 2015: 2,900 miles in 2015; 8,000 miles in 2016; 9,000 miles on their first transatlantic in 2017; 7,000 miles to Svalbard in 2018; acquiring the Swan 59 Ice Bear in 2019; 12,000 miles in 2020; and 31,000 miles in 2025 across Falken and Adrienne.

The platform accesses the ECMWF ERA5 reanalysis database, which archives global surface data at 6-hour intervals back to 1940. This telemetry enabled Schell and Davis to review their June 2019 passage aboard Ice Bear from Lunenburg to St. John’s, Newfoundland. Schell recalled inviting the forecaster offshore: “Jeremy, you do all this forecasting from a desk. You got to see what it feels like when you’re in it.”

Approaching a Newfoundland fjord in fog, Ice Bear motored at 5.6 knots in 6 knots of westerly wind. The crew anchored in the fjord to wait out an approaching low and let fog clear before entering the iceberg zone. On June 22 at 2:00 pm, the boat sat east of the low center in south-southeasterly winds. By 8:42 am the next morning, the wind shifted west behind the low, clearing the way for departure.

The offshore run toward Saint-Pierre brought demanding sailing. Winds blew at 27 to 35 knots with gusts over 40 knots and 2.7-meter (10-foot) seas. Davis took his first offshore helm watch as Ice Bear ran off the wind. Entering the iceberg grounds, water temperatures dropped to 38 degrees Fahrenheit, while air temperatures stayed in the 40s. Schell logged: “Fastest 100 miles we’ve ever sailed. Beautiful clear skies and stars, but cold temps outside now in the 40s.”

The debrief also underscored model limitations with microscale features. During a 2019 transatlantic on Isbjørn, a subtle kink in forecast wind barbs materialized as an unforecast squall with 60 knots of wind for an hour, forcing the crew to run downwind bare poles at 10 knots. Localized outflow boundaries—such as 30-knot gusts in the Old Bahama Channel—regularly fall between model grid points, demonstrating why mariners must combine macro climatology with diligent watch-keeping.

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