Tropical Depression Twenty-One (2023)

Storm Active: October 23-24

Around October 20, a broad area of low pressure in the far southwestern Caribbean sea began to organize. It drifted very slowly westward and became more concentrated, all the while bringing heavy rains to the neighboring central American countries. During the afternoon of October 23, it was designated Tropical Depression Twenty-One. There was no time for the system to develop any more, however, because it made landfall that very night in central Nicaragua. The main impact was heavy rainfall. Twenty-One dissipated by the next morning.

The image above shows Twenty-One shortly after formation.

Twenty-One only became a tropical cyclone less than 12 hours before landfall in Nicaragua.

Hurricane Tammy (2023)

Storm Active: October 18-26,27-29

Around October 10, yet another late season tropical wave entered the eastern tropical Atlantic. The system gained organization as it moved westward and appeared to be close to tropical depression status on October 14. However, no well-defined center formed, and conditions became a little less favorable over the next few days. Thunderstorm activity in association with the broad low became more diffuse, and it took even more time for it to regroup. It wasn't until October 18 that the system finally was upgraded to Tropical Storm Tammy. At that time, it was 1000 kilometers east of the Windward Islands.

Tammy developed a fairly impressive central dense overcast and had good inflow on satellite imagery, but the vortex also showed clear tilt and was elongated northwest to southeast. This limited significant strengthening in the short term, but aircraft reconnaissace did find that Tammy was producing sustained winds of around 60 mph on October 19, making it a fairly strong tropical storm. The next day, the cyclone reorganized somewhat and developed a very small core. This led to a short burst of intensification and Tammy was a category 1 hurricane late that morning. The storm gradually turned toward the northwest as it approached the Lesser Antilles. Its center passed just to the east of Martinique and Dominica on the morning of October 21. Though scattered heavy rainfall was widespread across the nearby islands, the small windfield of Tammy kept hurricane-force winds off of land for the most part.

After a bit more strengthening, Tammy reached its first peak intensity of 85 mph winds and a pressure of 988 mb later on the 21st. The center made a direct landfall in Barbuda that evening, bringing severe impacts to the small island. After that, the storm moved gradually away from the Caribbean islands, though rainfall lingered from the outer bands through October 22. The storm continued to round the periphery of the subtropical ridge and turned north. It maintained category 1 strength and continued to exhibit a small but powerful area of central convection.

In the subtropics, Tammy turned northeast and encountered a more diffluent upper-level environment. This began another period of strengthening late on October 24 and an eye appeared on satellite imagery the next morning. Tammy soon reached its peak intensity as a category 2 hurricane with 105 mph winds and a minimum pressure of 965 mb. Later in the day, stronger shear set in as the storm began to interact with a nearby front and weakening began. The storm underwent a rather quick extratropical transition early on October 26. Little more than a day later, though, ex-Tammy separated from the front and became a tropical cyclone again. At that point, it was estimated to be a strong tropical storm in intensity.

The storm remained very compact, with deep convection occurring only very close to the center. Therefore, even though it was rather close to Bermuda, the island did not receive any severe impacts. It moved south of east away from Bermuda after that and gradually weakened due to dry air around it. Warm ocean waters could not counteract the unfavorable atmospheric environment and Tammy lost deep convection by late on October 28. It became post-tropical for the final time early on the 29th.

The image above shows Hurricane Tammy at peak intensity as a category 2 on October 25.

Tammy's primary impacts were to the Leeward Islands.

Tropical Storm Sean (2023)

Storm Active: October 10-15

On October 6, a late-season tropical wave entered the Atlantic. By October, the Intertropical Convergence Zone retreats southward toward the equator, so tropical waves tend to form at lower latitudes. This system was no exception; it tracked westward over the next couple of days at around 7.5° N, passing well to the south of Cabo Verde. Though the wave was producing widespread thunderstorms, it took time to spin up. Late on October 10, it had acquired enough organization to be designated Tropical Depression Nineteen. The next morning, it was upgraded to Tropical Storm Sean.

A gap in the ridge to Sean's northwest allowed it to turn right and gain some latitude over the next few days. Due to wind shear, the storm remained disorganized. It even weakened to a tropical depression late on October 11 before regaining tropical storm status the next morning when a larger area of convection developed on the east side of the circulation.

Shear over the system relaxed somewhat after that, but Sean faced the new obstacle of very dry air aloft. This proved to be a more potent adversary for the cyclone; it weakened and grew increasingly shallow on the 14th, returning to tropical depression status. Intermittent convective bursts allowed the storm to retain its status as a tropical cyclone into the 15th, but they became steadily less organized. The decaying storm also turned back toward the west in the low-level flow. Late that day, the system became a remnant low. Not long after, the remnants dissipated east of the Leeward Islands.

The image above shows Sean as a disorganized tropical storm on October 13.

Sean did not affect any land areas.