Hurricane Isaias steadily intensifying over record-warm Gulf waters » Yale Climate Connections

by Jeff Masters and Bob Henson, Yale Climate Connections
October 8, 2026

Hurricane warnings are flying for portions of Mississippi, Alabama, and the Florida Panhandle as steadily intensifying Hurricane Isaias heads towards an anticipated Friday night landfall. Isaias became the first hurricane of the 2026 Atlantic hurricane season on Wednesday night, 57 days later than the typical formation date for the season’s first hurricane. This was the latest date since 1914 for the Atlantic’s first hurricane (no hurricanes and just one tropical storm occurred that year). Isaias’s 40 mph increase in intensity in the 24 hours ending at 5 a.m. EDT Thursday exceeded the definition for rapid intensification of a 35-mph increase in winds in 24 hours. By Thursday afternoon, Isaias was a Cat 2 hurricane.

Isaias could peak as a major Category 3 hurricane on approach to the northern Gulf Coast Friday, though significant weakening is expected in the few hours before landfall and/or just after landfall. Such weakening would limit wind damage, but storm surge damage will be significant regardless of any last-minute weakening.

At 5 p.m. EDT Thursday, Isaias was located about 325 miles (525 km) south of the mouth of the Mississippi River, headed northeast at 12 mph (19 km/h), with maximum sustained winds of 100 mph 160 km/h) and a central pressure of 975 mb, making it a Category 2 hurricane. Wind shear was a moderate 15-20 knots, and sea surface temperatures (SSTs) were record-warm, near 30-31 degrees Celsius (86-88 degrees Fahrenheit).

Isaias was embedded in a adequately moist atmosphere with a mid-level relative humidity of 60%. Satellite images Thursday afternoon and data from the Hurricane Hunters showed that Isaias was steadily intensifying, with a prominent eye clearing out.

As we wrote Tuesday, sea surface temperatures averaged across the Gulf are the warmest on record for this point in October, and they’re running between 30 and 31 degrees Celsius (86-88 degrees Fahrenheit) along the disturbance’s path. Human-caused warming has made such unusual readings several hundred times more likely over the western Gulf, according to Climate Central’s Climate Shift Index.

Track forecast for Isaias

The standard operational models and ensembles, such as the European, have been increasingly adopting the ideas from the AI ensembles, such as Google’s AI-based DeepMind model, showing a faster-moving hurricane making landfall further east in the Florida Panhandle. It now appears that the center of Isaias is most likely to cross the coast near the Alabama/Florida border, very near Pensacola.

Intensity forecast for Isaias

For the remainder of Thursday, Isaias should have favorable conditions for intensification, with record-warm waters, moderate wind shear, and a moist atmosphere. There is some dry continental air flowing off the coast of Texas invading the west side of the Gulf, but so far the hurricane has been able to isolate its core from the dry air. The 18Z Thursday run of the SHIPS and DTOPS statistical models were ho-hum about the possibilities for rapid intensification, giving a 10-11% chance of a 35-mph increase in Isaias’ winds in the 24 hours ending at 12Z (8 a.m. EDT) Friday.

The traditional high-resolution hurricane models on Thursday generally predicted (Fig. 1) that Isaias would peak as a Cat 2 hurricane. Google’s DeepMind model was more aggressive, predicting a Cat 3 peak. NHC has Isaias peaking as a high-end Cat 2 hurricane with 110 mph winds on Friday morning, when it will be traversing an eddy of deep, warm water that could aid intensification.

The wind shear affecting Isaias is from strong upper-level winds out of the west-southwest, and this shear will increase by Friday morning to the high range, 25-35 knots, according to the SHIPS model. A secondary smaller trough of low pressure is predicted to merge with the large central U.S. trough on Friday afternoon or evening, causing wind shear to rise to a very high 40-55 knots. At the same time, a flow of dry air on the back side of Isaias will be wrapping toward the core from the west. The combination of very high wind shear and dry air should be able to breach the storm’s core, but it is uncertain if this will occur a few hours before landfall or just after landfall. The farther to the west and slower that Isaias tracks, the closer the storm will be to the influences of this high wind shear and dry air, resulting in a weaker storm. A faster and more easterly-tracking storm will tend to be stronger. The most likely landfall intensity of Isaias has an unusually large range, from a strong tropical storm to a strong category 2 hurricane.

Major Atlantic hurricanes during a strong El Niño: a rare breed

If Isaias does achieve major hurricane strength, it will join a rare cadre of Atlantic storms that have managed to do so during strong El Niño conditions. Since records of NOAA’s Relative El Niño Index (RONI) began in 1950, only four years have seen “strong” El Niño conditions (defined as the RONI index reaching 1.5°C or higher) during July-August-September: 1965, 1997, 2015, and now 2026. Only four major hurricanes were observed in the Atlantic those years – one for each year – as opposed to the three major hurricanes one would expect in a typical Atlantic season based on 1991-2020 climatology.

Betsy 1965: Cat 4, 130 mph. Made landfall as a Cat 3 in the Florida Keys and Cat 4 in Louisiana.
Erika, 1997: Cat 3, 125 mph winds. No landfall.
Danny, 2015: Cat 3, 125 mph. No landfall.
Joaquin, 2015: Cat 4, 140 mph. Made a Cat 4 landfall in the Bahamas, and as a tropical storm in the Leeward Islands.

Storm surge is a major concern

Storm surge is likely to be the main damaging impact of Isaias. The trough of low pressure affecting Isaias at landfall will inject considerable energy into the storm, significantly broadening its wind field and driving a damaging storm surge far to the east of where the center makes landfall, even if the core collapses and Isaias hits the coast as a tropical storm.

A storm surge of about two feet has been impacting southwestern Louisiana since Wednesday morning at Southwest Pass, Louisiana (near the mouth of the Mississippi River). Pensacola, FL, has been getting about one foot of storm surge since Wednesday morning. The surge has already been causing street flooding in one of the most vulnerable barrier islands in the U.S., Alabama’s Dauphin Island.

Tidal range in the Florida Panhandle at Pensacola is normally about two feet between low and high tide, but on Friday and Saturday, some of the lowest tides of the month are expected, with a tidal range of only about half a foot. Thus, the timing of when Isaias makes landfall won’t make a big difference for how much storm surge damage occurs. Tide gauge records at Pensacola began in 1923.

Watch for high winds

As with any landfalling Atlantic hurricane, wind damage will be highest in the eyewall on the right side of where the center makes landfall. The rapid forward speed of Isaias will spread damaging winds well inland, though, and a High Wind Watch has been issued for northern Alabama and Georgia, plus the Appalachian Mountain regions of North Carolina and Tennessee. Significant power outages are possible across this heavily treed area.

Rainfall could cause flooding

Rainfall from Isaias will be limited by its relatively fast forward speed, which is expected to be about 15 mph at landfall. In addition, the rains will be falling on dry soils; portions of the coast expected to receive the heaviest rains are in the “Abnormally Dry” to “Moderate” drought categories, according to the latest U.S. Drought Monitor. Portions of the South to the northwest of where Isaias makes landfall will have increased wildfire risk from the storm’s strong winds, where no rain falls.

Nevertheless, the National Weather Service’s Weather Prediction Center is maintaining its “Moderate” (threat level 3 of 4) of excessive rain leading to significant flash flooding for Friday through early Saturday for South Alabama and the western Florida panhandle, including the cities of Mobile and Pensacola.

Tornado threat could be a concern

Tornadoes are a concern with any landfalling storm, and Isaias looks particularly likely to be a tornado threat. The maximum risk will likely be in the Florida Panhandle Friday night within the rainbands on the east side of the center. The tornado threat will spread to Georgia, eastern Alabama, and parts of South Carolina on Saturday.

Rachel and Simon: a rare twin landfall event on Mexico’s Pacific coast this weekend

It’s not every year that significant hurricane landfalls occur in the Gulf of Mexico and on Mexico’s Pacific coast within a day or two of each other, as will be happening this weekend. And in this case, a third landfalling named system is in the mix – one that’ll be weakening fast but could still push moisture into the Southwest United States.

Both of the Pacific landfalls are predicted for Saturday night. The bigger threat of the two by far is fast-strengthening Tropical Storm Simon, which was nearing hurricane strength at 5 p.m. EDT Thursday about 230 miles (370 km) south of Manzanillo, Mexico. After it moves slowly west on Thursday night, Simon will take a sharp north turn on Friday. With the classic ingredients in place – light to moderate wind shear, very warm sea surface temperatures around 29 degrees Celsius or 84 degrees Fahrenheit, and a moist mid-level atmosphere – Simon is expected to intensify rapidly.  

Simon poses a prediction challenge similar to the one Isaias has posed:  should forecasters go with the standard physics-based models or the AI-based models? As with Isaias, the physics-based and AI-based model ensembles for Simon are on the left- and right-hand sides of the guidance envelope, respectively. With the recent good performance of AI models in mind, NHC’s official forecast for Simon is leaning rightward as well. Such a track would take Simon in the general direction of the Bay of Banderas, potentially passing over or near Puerto Vallarta, Mexico. Simon is predicted to reach Category 4 strength on Saturday and remain there until landfall, so residents should prepare for the impacts of a major hurricane.

Torrential rains of 8-15 inches, with isolated amounts up to 25 inches, will cause life-threatening landslides and flash floods along and near the coasts of Jalisco and Michoacán states. Huge surf can also be expected, and a significant storm surge could strike depending in part on the exact angle of Simon’s approach.

Rachel’s landfall near the north end of Baja California Saturday night or Sunday morning should be much more placid. As of Thursday evening, dry air (a mid-level relative humidity around 30 percent) continued to invade slow-moving Rachel’s circulation, and wind shear will start to increase on Friday. Rachel was already little more than a huge cloud swirl on Thursday afternoon, with just a few bands of convection (showers and thunderstorms) evident on satellite imagery, but Rachel’s winds will be slow to diminish. As of 5 p.m. EDT Thursday, Rachel’s top sustained winds were still 65 mph (110 km/h), and gale-force winds extended out up to 115 miles (185 km) from Rachel’s center.

Rachel will be gradually spinning down as it begins to accelerate northeastward on Friday and Saturday, and it will most likely come ashore on Saturday night as a weak tropical storm, perhaps getting as far as southern Arizona before evolving into a windy post-tropical low. Either way, Rachel’s extensive field of moisture will be swept into the flow around a large upper low setting up in the western United States. A multi-day stretch of enhanced rainfall can be expected across much of the West, as moisture from post-landfall Simon eventually enters the mix toward Arizona and New Mexico. A slight risk (level 2 of 4) of excessive rain leading to flash flooding is in place from Sunday morning into early Monday across the Colorado River basin, including parts of southeast California, western Arizona, and southern Nevada and Utah.

Swells partly generated by Rachel will build along the coast of Southern California and northern Baja California through the weekend. These swells are likely to cause life-threatening surf and rip current conditions as well as minor to moderate coastal flooding. 

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