Sean Forms Over the Eastern Atlantic with Another Area to Watch Close Behind

Hurricane Lidia’s remnants will merge with a messy non-tropical Gulf system, bringing gusty winds and stormy weather to the northern Gulf Coast starting today

As we’ve written in previous newsletters, Cabo Verde season – the busiest part of the hurricane season so named for the islands off Africa where big hurricanes have their start – typically winds down quickly in October. The tropical waves that commonly develop over the tropical Atlantic in September taper off and begin to lay dormant on their journey west. At least that’s what typically happens.

Average number of tropical systems that form from Cabo Verde tropical waves (African Easterly Waves or AEWs) by month. By October, the number of tropical waves that develop into tropical depressions, storms, and hurricanes quickly tapers off. Credit: Erica Staehling/Princeton University

The extra warmth across the deep tropical Atlantic – the warmest waters on record for the time of year – have extended the Cabo Verde part of the hurricane season into extra innings.

Invest 92L, an eastern Atlantic tropical wave that we first began tracking last Thursday, got the upgrade to Tropical Storm Sean – the 18^th named storm of the season – late last night. As we’ve discussed this week, the storm isn’t expected to strengthen much or pose any threat to land. The official forecast weakens Sean over the central Atlantic by early next week.

Another impressive tropical wave just west of Africa behind Sean also shows some potential for development. For the time being it’s not something to be concerned about, but since it will be moving due west and not immediately turning out, we’ll want to keep tabs on it for the islands into late next week.

Lidia rapidly strengthens, striking Mexico as the country’s third strongest eastern Pacific hurricane

Hurricane Lidia in the eastern Pacific outran the forecasts yesterday, rapidly strengthening from a 75 mph Category 1 to a powerful 140 mph Category 4 hurricane in the 24 hours leading up to landfall. This rapid rate of strengthening over such a short period occurs less than 1% of the time, but unfortunately with Lidia it coincided with the hurricane’s approach to Mexico.

Lidia came ashore about 40 miles south of Puerto Vallarta in west-central Mexico around 8 PM ET Tuesday as the third strongest eastern Pacific hurricane to strike the country.

Although Lidia’s circulation was quickly torn apart by the high mountains across inland Mexico, its leftovers will fuse with a frontal low over the northern Gulf of Mexico today, enhancing rainfall across the northern Gulf Coast. While the Gulf system isn’t expected to develop into a tropical cyclone, it will bring tropical storm gusts (up to 40+ mph) and locally heavy rainfall to the immediate coast from south Louisiana to the Florida panhandle starting later today.