If you had on your 2022 weird-weather Bingo card that the major U.S. city that would come closest to a hurricane during the first half of the 2022 hurricane season would be San Diego, then you’re psychic. With hurricane season reaching its halfway point on Saturday, the closest any Atlantic hurricane has come to a major U.S. city is 900 miles: That’s the distance Hurricane Earl was from Miami on September 6. But in the eastern Pacific at 11 a.m. EDT September 8, Hurricane Kay lay just 500 miles south-southeast of San Diego. Steadily closing the gap, the hurricane is predicted to remain at hurricane strength until Thursday night, when it will be just 350 miles from San Diego. While Kay is not expected to reach California as a tropical storm, the state will see a rare constellation of hurricane-related effects – including rains both helpful and harmful.
A channel of deep moisture en route to California
As of 11 a.m. EDT Thursday, Kay was a category 1 storm about 60 miles southwest of the coast of Mexico’s Baja California Peninsula, with top sustained winds of 85 mph. Heavy rains from Kay were soaking Mexico’s Baja Peninsula, and an outer spiral band from the hurricane had moved into Southern California, bringing rain to the San Diego and Los Angeles areas. Kay had moved over cool 23 degree-Celsius (73°F) waters associated with the cold southward-flowing California Current, so a gradual weakening of the top winds is expected. However, Kay will remain a large, sprawling storm capable of widespread impacts.
Kay’s north-northwest motion of 15 mph is roughly parallel to the Baja Peninsula. On this track, Kay is predicted to move over or near the sharp westward jut of mid-Baja on Thursday evening, most likely as a borderline category 1 hurricane/tropical storm. This sparsely populated area is home to Mexico’s largest wildlife refuge, the El Vizcaíno Biosphere Reserve. The largest town is Bahía Tortugas (pop. 2,300), which sits on a natural south-facing harbor. Given Kay’s angle of approach and its unusually large wind field, there could be significant storm surge along the coast near and east of Kay’s track. Few hurricanes are known to have struck near Bahía Tortugas; the most recent is Nora (1997).
Kay’s most distinctive feature is its expansive plume of moisture. The hurricane is embedded in a very moist air mass, with mid-level relative humidity around 70%. This moisture will be funneled up the Gulf of California as Kay continues moving north-northwest. Precipitable water values (the amount of water vapor in a vertical column above a given point) are in the 2-to-2.5-inch range over a large area surrounding Kay. Rainfall amounts of 6 to 10 inches are possible throughout Baja California, with localized totals of 15 inches on the peninsula and up to 6 inches on the far west Mexico mainland, bringing the risk of flash floods and mudslides in mountainous areas.
Heavy desert rainfall expected as Kay proceeds
There’s high confidence that Kay’s large circulation will move close enough to Southern California for a variety of impacts, and also high uncertainty on exactly how things will play out. Climate scientist Daniel Swain wrote an excellent blog post Wednesday night explaining many of the factors in play.
The record-smashing heat wave that’s led to unprecedented September heat across the western U.S. – including a number of all-time highs for any month – is one factor in the mix. The heat has been stoked by a sprawling upper-level high (record-strong for September at some locations) extending from the western U.S. into the Northeast Pacific. That high will also help block Kay from moving directly into the southwestern states, which is a more typical track taken by recurving northeast Pacific hurricanes.
Instead, as Kay steadily weakens from cooler waters, drier air at mid-levels of the atmosphere, and land interaction with the Baja Peninsula, the storm will be steered more by the flow of air near the surface, which is moving clockwise around the mighty high-pressure system to the north. Kay will be forced into a slow leftward bend, arcing away from the coast to the southwest of the California/Mexico border. The closest Kay’s center will come to California is about 100 miles to the southwest of the border with Mexico late on Saturday night.
Kay’s winds will weaken as it traverses the relatively cool waters just off the coast of northern Baja (SSTs around 23 degrees Celsius or 73 degrees Fahrenheit) while much of the circulation sits over the peninsula. These waters are about 1-2 degrees Celsius (1.8-3.6°F) above average, allowing Kay to penetrate unusually far north, but Kay will still be a weakening tropical storm as it reaches the northernmost point in its multi-day loop. That point is expected to stay southwest of San Diego, but it could be close enough to produce gusty offshore winds and exceptionally warm temperatures (especially at night) near the coast. In its 11 a.m. EDT Thursday wind probability forecast, the National Hurricane Center gave San Diego a 13% chance of experiencing tropical storm-force winds.
The higher-confidence part of the Kay forecast is for an infusion of rich moisture into much of California, as moist southerly and southeasterly flow wraps around the northeast side of Kay’s broad circulation. By the weekend, precipitable water values could be at near-record levels for September across much of California east and south of Los Angeles. Clouds and rains will provide welcome relief from recent torrid temperatures, but the downpours could be heavy enough to produce flash flooding, especially along east-facing slopes of coastal mountains from L.A. To San Diego. Some rains may work their way as far north as central California, although the moisture may also enhance risks of lightning and wildfire starts.
The National Weather Service’s Weather Prediction Center, WPC. took the unusual step of issuing a “moderate” risk outlook for excessive rains leading to flash flooding on Friday and Saturday over parts of the far Southern California desert. “It’s never a good thing to get too much rain all at once, a trait all too common among slow-moving tropical storms,” WPC warned, noting that the amount of water vapor in the atmosphere was expected to be an amazingly high five standard deviations above normal for this time of year.
Tropical cyclones: rare visitors to California
Few tropical storms and hurricanes have affected California. Since 1850, Southern California has experienced gale-force winds from seven tropical cyclones or their remnants. In general, the Pacific waters off the coast of Southern California and far northern Baja California are too cool to sustain a tropical storm or hurricane for very long, because of the cold waters of the southward-flowing California Current. In any event, most tropical cyclones from the northeast Pacific recurve before they reach the latitudes of San Diego or Los Angeles. Only two systems are known to have made it far enough north, while still offshore, to bring tropical storm conditions to the coast of Southern California:
1858: A northeast Pacific hurricane accelerated north-northeast in early October 1858, approaching San Diego on October 2 before veering westward, not unlike the track projected for Kay. The city had only a few hundred permanent residents at the time.
Independent scholar Michael Chenoweth teamed with Chris Landsea (NHC) in 2004 for an analysis of the storm (see PDF). At the New San Diego port, the barometric pressure dropped from 29.91 inches at 7 a.m. PST on October 2 to 29.50 inches (994 millibars) at 2 p.m., which according to Chenoweth and Landsea, suggests winds of at least 65 mph. The weather observer remarked: “A great storm, causing the air to be filled with dense clouds of dust, some of the houses were unroofed and blown down, trees uprooted, and fences destroyed.” Along these lines, a San Diego correspondent for the Daily Alta California reported that “several very heavy gusts of wind came driving madly along, completely filling the whole atmosphere with thick and impenetrable clouds of dust and sand …. this continued for a considerable length of time, the violence of the wind still increasing, until about one o’clock, when it came along in a perfect hurricane, tearing down houses and everything that was in its way.”
1939: A northeast Pacific hurricane moved steadily north and then northeast, weakening to tropical storm strength not long before making landfall near San Pedro, California, on September 25. The trajectory pushed great volumes of moisture against the coastal ranges from Los Angeles southward, leading to widespread flooding from torrential rains that totaled 11.60 inches (295 millimeters) at Mount Wilson and 5.66 inches (133 millimeters) in downtown Los Angeles. Wind gusts reached 65 mph at Long Beach, and at least 48 people were killed, many of them aboard two ships that sank near the coast.
“The storm turned the sea into a raging force as huge waves pummeled the Alamitos Peninsula and Belmont Shore, yanking 10 homes off their foundations and washing them out to sea, while reducing scores of others to driftwood kindling,” the Long Beach Post reported in a 2019 retrospective. As with the current scenario with Kay, the tropical storm arrived after an intense, prolonged heat wave.
Earl on course to brush Bermuda, expected to become a major hurricane
At 11 a.m. EDT Thursday, Hurricane Earl was spinning through the Northwest Atlantic about 230 miles south of Bermuda, heading north-northeast at 13 mph. Earl’s top sustained winds increased to 105 mph on Thursday morning, a harbinger of more sustained strengthening just around the corner.
Earl’s gradually recurving path toward the north-northeast will take it just southeast of Bermuda, close enough for an 82% chance of tropical-storm-force winds, but just a 3% chance of hurricane-force winds. Swells from Earl may extend all the way to parts of the U.S. East Coast, where rip currents will be a hazard into the upcoming weekend. Radar from Bermuda showed Earl’s rains were already affecting the island on Thursday afternoon. Satellite imagery showed that wind shear over Earl had relaxed significantly, and the hurricane is now rather symmetric, with an impressive eye surrounded by clouds with very cold tops.
As Earl travels across unusually warm waters for the Atlantic subtropics, with sea surface temperatures around 29 degrees Celsius (84 degrees Fahrenheit), the relaxing wind shear will provide Earl with a window of opportunity to strengthen noticeably. The NHC forecast at 11 a.m. EDT Thursday brings Earl up to the threshold of category 4 strength (130 mph sustained winds) by Friday night at the remarkably high latitude of 37°N. The only analog for a category 4 storm within 200 miles of Earl’s predicted Friday night location is Hurricane Sam (2021) – but Sam had reached cat 4 strength well before reaching such a high latitude.
As Earl continues northeast over the weekend, it will interact with a strong midlatitude storm system that should hasten Earl’s transition to post-tropical status in the open Atlantic on Saturday night.
Danielle finally dies
The record-warm waters of the mid-latitude North Atlantic giving Earl a boost also nurtured Hurricane Danielle, which maintained hurricane strength at latitudes above 37°N for a record-long period of time – five days (see Tweet above by Steve Bowen). Danielle finally weakened to a tropical storm at 5 a.m. EDT Thursday, and NHC declared it post-tropical at 11 a.m. NHC predicted that ex-Danielle could affect Spain or Portugal on Tuesday with sustained winds near 35 mph.
Two more tropical waves to watch
A tropical wave designated as Invest 95L, about 1,000 miles west-northwest of the Cabo Verde Islands on Thursday afternoon, was headed west to west-northwest at 15-20 mph. Satellite images on Thursday afternoon showed that 95L had a well-defined surface circulation, but only a few heavy thunderstorms, which were limited to the system’s east side by strong wind shear of 20-30 knots. 95L will have marginally favorable conditions for development through Friday, needing only a modest increase in its heavy thunderstorm to become a tropical depression.
By Saturday, 95L will move into a region with drier air, which should limit further development. The wave is predicted to move into a region of the central Atlantic from which few tropical cyclones ever end up making it to North America. The long-range predictions from the GFS and European model ensembles unanimously show that this wave will recurve to the north by early next week. In its 8 a.m. EDT Thursday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 70%. The next name on the Atlantic list of storms is Fiona.
A new tropical wave that emerged from the coast on Thursday morning is predicted to move west-northwestward on a path similar to that of 95L. Although the wave has already developed a broad rotation, dry air to its north will hamper development. It is too soon to determine if it will end up being a concern for any land area. In its 8 a.m. EDT Thursday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 0% and 30%, respectively.
A new typhoon brewing in the western Pacific
In the western Pacific, Tropical Storm Muifa developed on Wednesday, well east of the Philippines; Muifa is a threat to develop into a major typhoon that will affect Japan’s Ryukyu Islands this weekend. At 8 a.m. EDT Thursday, the Joint Typhoon Warning Center (JTWC) pegged Muifa’s top winds at 50 mph (1-minute average), moving west at 12 mph. The Japan Meteorological Agency put Muifa’s intensity at 45 mph (10-minute average sustained winds).
Muifa had very favorable conditions for intensification on Thursday, with sea surface temperatures of 30-31 degrees Celsius (86-88°F), light wind shear of 5-10 knots, and a moist atmosphere. The Joint Typhoon Warning Center 11 a.m. EDT Thursday advisory called for rapid intensification of Muifa into a major typhoon with 115 mph winds by 0Z Saturday, peaking at 125 mph winds by Sunday. Weakening is expected on Sunday as Muifa crosses the cold water plume left behind by category 5 Super Typhoon Hinnamnor. Muifa is expected to turn more to the north-northwest into a region of higher wind shear and move through Japan’s Ryukyu Islands on Monday, and it could be a threat to China later in the week.
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