Jeff Masters Hurricane Blog

Tammy sweeps into Northern Leewards; Norma hammers Cabo San Lucas, Mexico » Yale Climate Connections

Saturday, October 21, brought a juxtaposition you don’t see often: in the Atlantic, Hurricane Tammy was moving through the Northern Leeward Islands, while in the eastern Pacific, Hurricane Norma was making landfall over southernmost Baja California, Mexico. Neither Tammy nor Norma was a major hurricane, but they both stood to bring significant impacts on either side of the Americas.

Hurricane Tammy lashing the Leeward Islands

Hurricane Warnings were up for much of the Leeward Islands on Saturday afternoon as a slowly-intensifying Hurricane Tammy gathered strength in the record-warm waters of the tropical Atlantic. Tammy is expected to be a category 1 hurricane as it passes near or over the northeastern Leeward Islands Saturday night into Sunday morning.

At 11 a.m. EDT Saturday, Tammy was located about 50 miles east-southeast of Guadeloupe, headed west-northwest at 8 mph with top sustained winds of 85 mph and a central pressure of 988 mb. Satellite images early Saturday afternoon showed that Tammy had a modest amount of heavy thunderstorms that were slowly growing more organized and more intense. Moderate wind shear of 10-20 knots out of the west was keeping Tammy’s heaviest rains and strongest winds confined to the east side of the storm; the strongest wind gusts observed at major airports in the Lesser Antilles Islands on Saturday morning were in the 30-40 mph range.

Figure 1. Track forecasts out to five days for Tammy from the 6Z Saturday, October 21, run of the GFS ensemble model (left) and European ensemble model (right). Individual forecasts of the ensemble members are the lines color-coded by the wind speed in knots they predict; red colors correspond to a category 1 hurricane. The models generally show that a stronger storm will miss the Leeward Islands, passing just to the northeast, while the predictions of a weaker storm tend to show a track through the islands, and a potential stall to the north of Puerto Rico in the case of the European model. The time in hours from the model initialization time is in gray text. (Image credit:

Forecast for Tammy

Conditions will be favorable for some modest intensification of Tammy over the next three days, with moderate wind shear of 10-20 knots, a reasonably moist atmosphere, and record-warm waters of 30 degrees Celsius (86°F), about 1-2 degree Celsius (1.8-3.6°F) above average. Rapid intensification is not likely; the 12Z (8 a.m. EDT) Saturday SHIPS model gave an 18% chance that Tammy would intensify by 35 mph in the 24 hours ending at 8 a.m. EDT Sunday.

Tammy has some modest support for intensification from the models, with the 6Z Saturday suite of regional hurricane models (HWRF, HAFS-A, HAFS-B, and HMON) showing Tammy passing by Barbuda, the most northeasterly of the Leeward Islands, with sustained winds as low as 60 mph (HAFS-A model) or as high as 105 mph (HAFS-B model). The timing of this passage was predicted to be between 11 pm. EDT Saturday and 2 a.m. EDT Sunday. It’s possible that Tammy will just miss making an official landfall in the Northern Leewards. As defined by the National Hurricane Center, landfall is defined as “the intersection of the surface center of a tropical cyclone with a coastline. Because the strongest winds in a tropical cyclone are not located precisely at the center, it is possible for a cyclone’s strongest winds to be experienced over land even if landfall does not occur. Similarly, it is possible for a tropical cyclone to make landfall and have its strongest winds remain over the water.”

Given the continued moderate westerly wind shear expected to affect Tammy during the next few days, most of the significant winds and rains of the storm will be to the east of the center, where heavy rains of 4-8 inches are predicted. Puerto Rico and the Virgin Islands are expected to be on the drier west side of Tammy, and receive lesser rain amounts. As of 11 a.m. EDT Saturday, no tropical storm watches or warnings were in effect for Puerto Rico or the U.S. Virgin Islands.

An intensifying eastern U.S. upper low is expected to force Tammy to recurve northward into the open Atlantic after the hurricane passes through the Leeward Islands, but it is unclear if this trough will be strong enough to fully capture Tammy and accelerate the storm to the northeast. A number of models now show Tammy stalling several hundred miles to the north of the Virgin Islands and Puerto Rico by mid- or late-week, which would potentially make Tammy a long-range threat to Bermuda. The National Hurricane Center is currently predicting that Tammy will peak as a category 1 hurricane with 90 mph winds on Sunday through Tuesday, but the uncertainty in both the track and intensity forecasts is high for Tuesday and beyond.

Figure 2. Visible satellite image of Hurricane Norma at 11:40 a.m. EDT Saturday, October 21, 2023. (Image credit: NOAA/RAMMB/Colorado State University)

Norma moving into Baja California near Cabo San Lucas

As of 11 a.m. EDT Saturday, category 2 Hurricane Norma was just 30 miles west-southwest of Cabo San Lucas with top sustained winds of 100 mph. Norma was moving north at 8 mph, a course that will bring its center across southernmost Baja California (the state of Baja California Sur) on Saturday afternoon and evening. Around 11 a.m. EDT Saturday, San José del Cabo International Airport reported sustained winds of 35 mph, gusting to 50 mph. Another reporting station near Cabo San Lucas observed sustained winds of 55 mph with gusts to 72 mph, according to the National Hurricane Center. High surf was pounding parts of Baja California Sur.

Increasing wind shear and increasingly dry air have gradually brought Norma down from the category-4 peak of 130 mph it achieved on Thursday, and further weakening is expected as Norma interacts with land on Saturday and Sunday. Norma will likely make landfall on the west coast of Baja California Sur just northwest of Cabo San Lucas, putting the city on the storm’s stronger right-hand side. A shift toward west-southwest steering flow will push Norma across the warm Gulf of California on Sunday, most likely as a tropical storm, and into Mexico’s Pacific Coast in the state of Sinaloa by late Sunday.

Figure 3. Radar image from the Los Cabos area at 1407Z (10:07 a.m. EDT) Saturday, October 21. (Image credit: Government of Mexico)

Satellite-based data and radar images show that dry air was leading to diminished rainfall on the south side of Norma as the storm approached on Saturday morning. Still, 6-12 inches of rain, with pockets of up to 18 inches, is possible as Norma moves over Baja California Sur on Saturday and Saturday night, with the risk of flash flooding and mudslides. Significant flooding may also occur in Sinaloa if Norma maintains its circulation as it treks across the Gulf of California. In fact, the GFS model suggests the peak rainfall from Norma will be along and near the Sinaloa coast, perhaps topping 20 inches or more in some spots, as Norma’s moisture is pushed upslope against the high, rugged terrain of the Sierra Madre Occidental range.

Figure 4. Hurricanes passing within 50 miles of Cabo San Lucas, Mexico. Nearly all of these are from the satellite-based dataset database that extends back to the 1970s. (Image credit: NOAA Historical Hurricane Tracks.)

Recent hurricane landfalls to affect Baja California Sur include Odile (2014) – which struck Cabo San Lucas directly as a category 3 storm with top sustained winds of 125 mph – and Olaf (2021), which made landfall near San Josè del Cabo, about 30 miles northeast of Cabo San Lucas, at category 2 strength with top winds of 105 mph. Odile’s catastrophic hit inflicted more than $1 billion (2014 USD) in damage in Mexico, most in Baja California Sur, and took 18 lives. Olaf caused one fatality and left about $10 million USD in damage.

North Indian Ocean heats up

In the north Indian Ocean, Tropical Cyclone Tej formed on Friday, and had already intensified into a category 1 storm with 75 mph winds by 8 a.m. EDT Saturday. The Joint Typhoon Warning Center (JTWC) predicts that Tej will take advantage of light wind shear and warm sea surface temperatures near 29 degrees Celsius (84°F) to rapidly intensify to a category 4 storm with 130 mph winds by Sunday.

By Monday, Tej is expected to pull dry air from the deserts of the Middle East into its circulation, resulting in rapid weakening. Landfall as a tropical storm near the Yemen/Oman border is predicted to occur near 12Z Tuesday. The 6Z Saturday run of the HAFS-A model was predicting that Tej would bring a long swath of rainfall in excess of 4 inches to the coasts of Yemen and Oman. Rains of this magnitude would cause extreme flash flooding in a desert region unused to such heavy rains.

The JTWC is also monitoring disturbance 92B in the Bay of Bengal, which has the potential to develop into a tropical depression by Monday, and potentially bring heavy rains to India, Bangladesh, and/or Myanmar by Tuesday.

Website visitors can comment on “Eye on the Storm” posts (see comments policy below). Sign up to receive notices of new postings here.

Source link