Hurricane Nolo takes another turn, Polo to bring deep tropical moisture to Southwest desert » Yale Climate Connections

by Irene Sans, Bob Henson and Jeff Masters, Yale Climate Connections
September 28, 2026

As we head into the final days of September, the Pacific remains prolific. We are still monitoring major Hurricane Nolo, an extremely powerful Category 4 storm southwest of the Hawaiian Islands, and major Hurricane Polo, while newborn Tropical Storm Rachel continues to intensify along a path similar to Polo’s. Yet another Pacific system is likely to form as soon as Monday evening, although it will likely not be a threat to land. And in the Atlantic, Hanna, another “fish storm” — of concern only to marine interests — has been born.

Polo approaches Baja California

The most immediate land threat is Polo. At 11 a.m. MST (2 p.m. EDT) Monday, Polo was centered roughly 85 miles (140 km) west-southwest of Cabo San Lazaro, moving northeast at around 10 mph (17 km/h). Maximum sustained winds were estimated near 115 mph (185 km/h), with a minimum central pressure of 964 mb, keeping Polo at the lower end of the Cat 3 intensity range. Significant wave heights near the hurricane were estimated to peak around 38 ft (11.5 meters).

Polo has maintained a remarkably well-defined inner-core structure considering its increasing latitude. On Sunday, satellite imagery showed very cold cloud tops surrounding the eyewall, while microwave imagery indicated a largely closed eyewall despite some erosion on its eastern side associated with residual easterly vertical wind shear. Earlier satellite intensity estimates supported winds above 120 mph before Polo subsequently weakened.

The hurricane is now entering a critical portion of its track – fortunately one that’s more straightforward than its earlier twists and turns, as steering currents have now solidified. A northeastward motion is taking Polo toward Baja California Sur, and the National Hurricane Center expects life-threatening hurricane-force winds and flash flooding across portions of Baja California Sur and later Sonora. Polo is expected to remain near major-hurricane intensity as it reaches Baja California Sur late Monday overnight before crossing the Gulf of California overnight and approaching mainland northwestern Mexico early Tuesday, perhaps still at hurricane strength.

Polo could rival the strongest landfalls on record for Baja California

Major hurricanes often prowl the waters just south and west of Baja California, but it’s highly unusual for one to strike the peninsula with as much strength as Polo was still packing on Monday. On the north and northeasterly tracks that lead to such landfalls, Pacific hurricanes are typically experiencing increasing wind shear, and dry air is often getting injected into the storm. Both of these conditions are affecting Polo on Monday, but the hurricane is starting off with such immense power that it could still be at or close to Cat 3 strength when it crashes ashore.

A total of nine Category 2 or stronger hurricanes have hit Baja California, Mexico since accurate records began in 1949. Only three of these were major hurricanes, and none of them struck the west side of the peninsula as majors. The strongest were Odile (2014) and Olivia (1967), both of which had winds of 125 mph (205 km/h) at landfall. After first striking the peninsula’s west coast as a tropical storm, Olivia actually intensified into a major hurricane while over the Gulf of California and then made a second landfall, this time arriving from the east, with 61 deaths reported. Odile came ashore on the southern tip of Baja California, near Cabo San Lucas, and raked most of the peninsula on a destructive overland track that lasted more than 24 hours. Odile caused more than $1.8 billion USD in damage and took 18 lives. The peninsula’s other major landfall was Kiko (1989), whose center came ashore at the southeastern tip of Baja California with top sustained winds of 120 mph (195 km/h) on a brief track with little damage.

The two strongest landfalls on record on the western Baja Peninsula coast near where Polo will be hitting are Norbert (2008) and Jimena (2009), both of which peaked as Cat 4s and then came onshore just south of Puerto San Carlos at Cat 2 strength with top sustained winds of 105 mph (170 km/h). Norbert, which approached on a recurving southwesterly track, damaged more than 20,000 homes and took 25 lives. Jimena approached from the south-southeast and made landfall just 18 hours after a two-day stretch at Cat 4 strength. Jimena dropped record rainfall of more than 20 inches in parts of Sonora state, taking five lives and causing more than $37 million USD in damage.

Rainfall and flash flooding related to Polo will extend far inland

Although Polo’s winds will gradually decrease as it moves over the tall mountains of the Sierra Madre Occidental, Mexico’s northwestern mountain range, this weakening does not immediately eliminate the hazard. Even as interaction with Baja California and eventually less favorable thermodynamic conditions disrupt the circulation, Polo’s wind field, deep tropical moisture, and forward motion can transport substantial moisture into northwestern Mexico. Orographic enhancement from winds pushing upslope against the terrain of Baja California Sur and mainland Mexico could locally increase rainfall considerably. Flooding from Polo is already being blamed for two deaths in Mexico, with one person missing.

From a meteorological perspective, Polo is also a good example of how steering currents become increasingly important for recurving eastern Pacific hurricanes. Rather than continuing harmlessly westward into the open Pacific, the cyclone has reached the western side of the subtropical ridge and is turning poleward and eventually northeastward. That steering evolution is what converts Polo from an open-ocean major hurricane into a significant land-impacting system.

Together with moisture from former Hurricane Odalys, moisture from Polo and its remnants will be propelled by southwest flow ahead of a large upper-level trough to fuel torrential rains and life-threatening flooding across the Southwest U.S. deserts and mountains. In addition, heavy rains will likely develop over the Southern and Central Plains later this week, as low-level moisture from the Gulf of Mexico enters the picture. The NOAA/NWS Weather Prediction Center has issued moderate-risk areas for excessive rains leading to flooding amid broader slight-risk areas for Monday, Tuesday, Wednesday, and Thursday.

Nolo: an extremely powerful central Pacific hurricane

Farther west, Hurricane Nolo has become the most intense cyclone on the planet. At 5 a.m. HST Monday, Nolo was about 535 miles (865 km) south-southeast of French Frigate Shoals, moving west-northwestward at approximately 13 mph (20 km/h). Maximum sustained winds were estimated at 155 mph (250 km/h), with a minimum central pressure of 929 mb, placing the cyclone near the upper end of Category 4 intensity.

Nolo possessed a well-established inner core with a doughnut-like annular structure, including a distinct eye around 35 miles (56 km) in diameter. Hurricane-force winds extended as far as roughly 40 miles (65 km) from the center in portions of the circulation, while tropical-storm-force winds extended outward up to 150 miles (240 km).

Annular structure often helps stabilize intense hurricanes, modulating any large swings in intensity. Only a slight strengthening would be enough to push Nolo into the Category 5 range, but wind shear will be increasing sharply from late Monday into Tuesday. The official NHC forecast on Monday morning kept Nolo as a strong Cat 4 storm before gradual weakening begins on Tuesday.

Nolo is moving along the southern and southwestern side of the subtropical ridge, producing its current west-northwestward trajectory. Eventually, the thermodynamic and upper-level environment should become less supportive, and gradual weakening is forecast. Fortunately for the populated Hawaiian Islands, the hurricane’s center is passing well southwest of the main island chain. However, the circulation is large enough that marine impacts extend far away from the eye, including an enormous wave field. A hurricane warning is in effect for eastern parts of Hawaii’s unpopulated Papahanaumokuakea Marine National Monument.

Tropical Storm Rachel gradually organizing south of Mexico

While Polo and Nolo command most of the attention – and rightfully so – Tropical Storm Rachel is another system worth watching closely. At 9 a.m. CST Monday, Rachel was located 230 miles (370 km) south-southwest of Acapulco. Maximum sustained winds had increased to approximately 50 mph (85 km/h), with a minimum central pressure slowly dropping to 999 mb.

The combination of scatterometer and satellite data gives considerably more confidence in both the location of the low-level circulation and the intensity estimate. Rachel is moving west-northwest at 8 mph (13 km/h), and that forward motion should gradually increase.

Rachel is being steered by a deep-layer ridge building across north-central Mexico, which should continue pushing Rachel toward the west-northwest. Consequently, the cyclone is expected to remain offshore of southern Mexico during the immediate forecast period, paralleling the coastline.

The key, however, is that environmental conditions appear supportive of additional organization. If the circulation remains vertically aligned, warm water, sufficient atmospheric moisture and a generally favorable upper-level wind pattern should allow Rachel to gradually strengthen. The National Hurricane Center expects the system to become a hurricane around the middle of the week. It will likely undergo gradual intensification rather than the explosive intensification we recently saw with Polo.

Still, Rachel will bring additional rounds of torrential rain over some of the same areas that were recently heavily impacted by Polo’s intense downpours. Coastal areas of the states of Guerrero and Michoacan could receive up to eight inches (200 mm) of rain in some spots, but generally between four and six inches (100–150 mm) are likely.

Another tropical cyclone could develop east-southeast of Hawaii

The Pacific basin may not be finished producing tropical cyclones. We are monitoring another broad area of low pressure well east-southeast of the Hawaiian Islands that continues to generate widespread showers and thunderstorms. Satellite-derived wind observations have indicated that the circulation is becoming better organized. As of 8 a.m. EDT Monday, the National Hurricane Center’s Tropical Weather Outlook assigned the disturbance a 90% probability of tropical cyclone formation within 48 hours. A tropical depression is therefore likely to form as soon as Monday evening. The expected motion is generally northeastward rather than toward Hawaii, which should keep the developing circulation well east-southeast of the islands.

The next name on the list is Simon. Once this system is named, the Eastern Pacific will have only six names left on the 2026 list. If all of the names on the list are used, a supplemental list of names established by the World Meteorological Organization will be used. This list and a similar one for the Atlantic were both adopted in 2021 after the Atlantic’s frenzied 2020 season generated 30 named storms, including nine that had to be drawn from the Greek alphabet. In the Pacific, the hyperactive 1985 and 1992 seasons generated 24 and 27 named storms, requiring the additions of Xina in 1985 and Ekeka, Hali, and Iniki in 1992 to the start-of-season storm lists.

The broader atmospheric state remains supportive enough that the Pacific cannot be treated as quiet behind these systems. For late September, there is still plenty of energy available across the basin — and right now, the atmosphere is making very efficient use of it.

In the Atlantic: Fay weakens and Hanna develops

Tropical Depression Fay continues to meander across the central Atlantic, about 1,265 miles west-southwest of the Azores. As of 11 a.m. EDT Monday, Fay had maximum sustained winds of 35 mph (55 km/h) and a minimum central pressure of 1011 mb, while moving south-southwestward at 9 mph (15 km/h). Increasing atmospheric stability and unfavorable upper-level convergence should cause convection to collapse, with Fay forecast to become post-tropical Tuesday and dissipate shortly thereafter.

Meanwhile, Tropical Storm Hanna has formed, also over the central subtropical Atlantic. NHC initiated advisories on Hanna on Monday morning after data confirmed that the broad area of low pressure had developed a well-defined circulation. As of 11 a.m. EDT, Hanna had maximum sustained winds near 45 mph (75 km/h) and a minimum pressure of 1006 mb, while moving eastward at around 17 mph (28 km/h). Hanna’s formation brings the 2026 Atlantic activity to seven named storms and zero hurricanes. On average, the Atlantic should see 10 named storms, five hurricanes, and two major hurricanes by September 28.

In his Eye on the Tropics Substack post Monday morning, Michael Lowry vividly illustrated the “tale of two seasons” going on this year in the violent Pacific and somnolent Atlantic.

Lowry pointed out that the patterns evident all season have only intensified as we move well past the midpoint of the Northern Hemisphere’s hurricane season. As of September 28, the accumulated cyclone energy, or ACE, for all of the Northeast Pacific’s activity this year was the highest for any season in records going back to 1991, at more than 150% of the average to date, whereas the Atlantic ACE was at the lowest levels in data going back to 1966, at less than 15% of the average to date.

Based on current activity, this contrast should only accentuate as we wrap up September this week.

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