Tropical Storm Zeta formed in the western Caribbean early Sunday morning, with the potential to rapidly intensify into a hurricane that will make two landfalls: one on Monday night in Mexico’s Yucatan Peninsula, near Cancan; and one on Wednesday along the central Gulf of Mexico coast of the U.S., between Louisiana and the Florida Panhandle.
If this seems like déjà vu, you’re not mistaken: Hurricane Delta had a nearly identical forecast during the first week of October.
At 11 a.m. EDT Sunday, Zeta was stationary, spreading heavy rain showers over Jamaica, Cuba, and the Cayman Islands, as seen on Cayman Islands radar. A personal weather station on the west tip of Jamaica at Negril recorded 3.12 inches of rain between midnight and 12:30 p.m. EDT Sunday.
Satellite images showed that Zeta was not well-organized, with only one prominent spiral band along the east side of the center, and only a modest amount of heavy thunderstorm activity near the center. Water vapor satellite imagery showed Zeta had good upper-level outflow on all sides, but dry air over the Gulf of Mexico was apparent, and has the potential to slow development in coming days.
2020 parade of record-early named storms continues
Zeta’s October 25 arrival marks the earliest date that any Atlantic season has produced its 27th tropical storm, topping the record held by Epsilon from November 29, 2005 (an additional unnamed storm was added to 2005’s tally after the season was over). In total, 24 of 2020’s 27 named storms set records as the earliest-arriving for their respective letter; only Arthur, Bertha, and Dolly fell short.
With over five weeks still to go in the 2020 Atlantic hurricane season, there already have been 27 named storms, 10 hurricanes, four intense hurricanes, and an accumulated cyclone energy (ACE) index of 136 (42% above average for the date). Colorado State University hurricane scientist Phil Klotzbach says the averages for this point in the season are 10.8 named storms, 5.6 hurricanes, 2.5 intense hurricanes, and an ACE index of 96.
If Zeta makes landfall in the U.S. as a named storm, it would be the record-breaking 11th storm to do so this season. Prior to 2020, the highest number of tropical storms and hurricanes to make landfall in the continental U.S. was nine, in 1916.
Track forecast for Zeta
Steering currents are weak in the western Caribbean, and Zeta is expected to move northwest at less than 10 mph through Monday morning. A ridge of high pressure will strengthen to the northeast of Zeta on Monday and Tuesday, forcing it on a northwesterly track at a faster 10-15 mph pace through the Gulf of Mexico. By Tuesday, an approaching trough of low pressure over the central U.S. is expected to turn Zeta more to the north or north-northeast, with a landfall along the central Gulf Coast on Wednesday expected.
If Zeta is a weak to moderate-strength tropical storm, an outcome suggested by the European model and its ensembles on Sunday morning, a landfall in Louisiana is more likely, since Zeta will be steered more by the low-level flow, tending to take the storm to the north. If Zeta is stronger, at hurricane strength, it will “feel” the upper-level winds out of the southwest from the approaching trough. In that case, it will track more to the north-northeast, resulting in a landfall potentially as far east as the Florida Panhandle.
Intensity forecast for Zeta
Zeta will have favorable conditions for intensification through Tuesday, with light wind shear of 5-10 knots, ocean temperatures of 29.5-30 degrees Celsius (85-86°F), and a moist atmosphere with a mid-level relative humidity of 60-70%. Zeta will be passing over waters in the northwest Caribbean having the highest heat content of any waters in the North Atlantic – a strong basis for rapid intensification.
However, for it to take advantage of these favorable conditions, Zeta needs to overcome its current poor structure. Northerly upper-level winds on Sunday afternoon were creating about 10 knots of wind shear over Zeta, causing the storm’s vortex to tilt with height, and keeping most of the heavy thunderstorm activity restricted to the south side of the center of circulation.
Most of the top intensity models predicted with their Sunday morning runs that Zeta would intensify into a category 1 hurricane by Monday night, when the storm will make its closest approach to Mexico’s Yucatan Peninsula and the western tip of Cuba. If Zeta manages to pass through the Yucatan Channel between Mexico and Cuba, the storm will likely continue to intensify as it enters the Gulf of Mexico. However, if Zeta makes landfall in Mexico or Cuba, considerable disruption to the storm will likely occur, and Zeta may need a day or more to reestablish its inner core and re-intensify.
The 12Z Sunday run of the SHIPS model gave good odds that Zeta will undergo rapid intensification: a 32% chance that it would intensify by 30 mph by Monday morning (three times higher than the climatological odds), and a 30% chance that it would intensify 75 mph by Wednesday, into a category 3 hurricane (six times higher than the climatological odds).
The official National Hurricane Center forecast called for Zeta to achieve category 1 hurricane status on Tuesday morning. A reasonable uncertainty range for Zeta’s intensity on Monday night, during its closest approach to western Cuba and northeastern Mexico, is 60-100 mph sustained winds.
On Tuesday night and Wednesday, when Zeta will be approaching the U.S. Gulf Coast, the storm will encounter more hostile conditions for intensification. Waters beneath the storm will be significantly cooler, wind shear will rise, and dry air over the Gulf will have the opportunity to wrap into its core. However, a strong band of upper-level winds to the north of Zeta will provide a more efficient upper-level outflow channel as the storm approaches the coast, helping counteract the increased shear.
Sally, Laura, and Delta all encountered similar conditions when they made landfall earlier this year; Sally and Laura did not weaken before landfall, but Delta did. Expect Zeta to behave more like Delta, since the ocean temperature structure of the Gulf is similar to what Delta encountered. Zeta could be anywhere between a strong tropical storm and a category 2 hurricane at landfall in the U.S., with the official NHC forecast of a weakening category 1 hurricane with 75 mph winds a reasonable prediction.
Hurricane Epsilon becoming extratropical
Hurricane Epsilon was steaming east-northeast at 30 mph at 11 a.m. EDT Sunday, and was maintaining hurricane status, with sustained winds of 75 mph and a central pressure of 960 mb. Epsilon is a large storm, with tropical storm-force winds that extended up to 380 miles to the north of the center. The large wind field was generating large swells, which will be affecting the U.S. East Coast and Atlantic Canada through Monday. Epsilon brought widespread rainfall amounts of 0.5-1.0 inches to southeast Newfoundland on Sunday morning, and winds gusted as high as 31 mph at the capital, St. Johns.
Epsilon will merge with a trough of low pressure to its north on Sunday afternoon and transition to a very powerful extratropical storm with winds near hurricane force. Its central pressure on Tuesday, October 27, when it will be a few hundred miles south of Iceland, could be between 935-940 mb, according to the 0Z Sunday runs of the GFS and European models.
Posted on October 25, 2020 (1:39pm EDT).