Tropical Storm Kay was declared post-tropical at 11 p.m. EDT Friday in the Pacific waters 145 miles southwest of San Diego, ending the life of a most unusual tropical cyclone.

After dumping up to six inches of rain in Mexico’s Baja Peninsula, causing damaging flooding, Kay approached very close to southern California as a tropical storm on Friday. Kay brought up to five inches of rain to the mountains east of San Diego, along with winds that gusted to 109 mph. Fortunately, no injuries or major damage are being reported in California from Kay, though the storm downed trees and power lines, and caused rock slides in the mountains. The winds from Kay did not lead to major spread of the wildfires burning in the state, and Kay’s rains helped damp down the fires – and provided valuable drought amelioration.

According to the National Weather Service, the following rainfall amounts were observed in southern California from Kay:

5.08″: Mt. Laguna
4.61″: Ranchita
4.44″: Volcan Mountain
4.04″: Agua Cliente
3.62″: Julian
2.64″: San Felipe
2.22″: Mount San Jacinto
0.65″: San Diego Airport

Most of San Diego’s rain (0.61 inches) came on Friday, making it one of the city’s ten wettest September days in 172 years of recordkeeping.

The top wind gust reported from Kay was 109 mph at a 6500-foot elevation on Cuyamaca Peak. Wind records are not routinely kept, but if confirmed this may be the strongest wind gust ever reliably reported in San Diego County.

Damage from Hurricane Kay to Puerto Penasco, Mexico, located at the northern end of the Gulf of California.

On Saturday afternoon, Kay’s remnant low was drifting slowly away from southern California, but will continue to bring showers to the San Diego and Los Angeles regions. Up to an inch of welcome rain is predicted for portions of southern California through Sunday.

Hurricane Earl dying in the North Atlantic

Hurricane Earl was barely a tropical cyclone late Saturday morning, as it raced north-northeast at 29 mph in the waters a few hundred miles south of Newfoundland. At 11 a.m. EDT Saturday, Earl was a category 1 hurricane with 90 mph winds, and was bringing strong winds to southern Newfoundland. St. Pierre on the island’s south coast reported sustained winds of 37 mph, gusting to 49 mph, on Saturday morning. (Update: Earl was declared a post-tropical cyclone by NHC at 5 p.m. EDT Saturday.)

Although NHC had predicted that Earl would peak as a category 4 storm, the hurricane underperformed, peaking at category 2 with 105-mph winds on Friday evening.

Earl is expected to complete the transition to a powerful extratropical storm by Saturday afternoon, leaving the Atlantic devoid of named storms – or even a tropical depression – on what has historically been the busiest day of the season, September 10.

Figure 2. Frequency of Atlantic hurricanes and tropical storms, 1851-2021. (Image credit: Michael Lowry, wplg.com)

Quiet in the Atlantic

The two tropical waves that were being monitored on Friday by the National Hurricane Center have been shredded by dry air and wind shear. The only wave worth tracking at this point is one that has not yet moved off the coast of Africa, but is expected to do so on Monday. This wave is predicted to move west to west-northwest at 15-20 mph over the eastern tropical Atlantic during the week, but has little model support for development. Dry air and wind shear will make this wave struggle to develop, like so many other systems have this hurricane season. In its 8 a.m. EDT Saturday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 0% and 30%, respectively. (Update: As of 8 a.m. EDT Sunday, the odds of this system developing in the 2- and 5-day periods have been lowered to 0% and 20%. No other systems were assigned probabilities by NHC.)

With the season half over, we have seen 5 named storms, 2 hurricanes, and 0 intense hurricanes – the first time since 2014 that no intense hurricanes have been observed by the season’s halfway point. The 1991 – 2020 climatological average for this point in the season are 8.1 named storms, 3.4 hurricanes, and 1.5 major hurricanes. The accumulated cyclone energy is currently 50% of average. The long-term runs of the GFS and European model show little change to the hostile conditions for hurricane development over the coming week, and it is a reasonable bet that we will be graced with no named storms during what is typically one of the busiest weeks of the season.

Figure 3. Forecast for Tropical Storm Muifa from the 11 a.m. EDT Saturday, September 10, advisory from the Joint Typhoon Warning Center.

Typhoon Muifa intensifying in the western Pacific

In the western Pacific, Typhoon Muifa is roiling the waters well east of the Philippines, and is a threat to develop into a major typhoon that will affect Japan’s Ryukyu Islands on Monday. At 8 a.m. EDT Saturday, the Joint Typhoon Warning Center (JTWC) pegged Muifa’s top winds at 100 mph (1-minute average), moving north-northwest at 7 mph. The Japan Meteorological Agency put Muifa’s intensity at 80 mph (10-minute average sustained winds).

Muifa had favorable conditions for intensification on Saturday, with sea surface temperatures of 28-29 degrees Celsius (82-84°F), light wind shear of 5-10 knots, and a moist atmosphere. The JTWC 11 a.m. EDT Saturday advisory called for rapid intensification of Muifa into a major category 4 typhoon with 130 mph winds by 12Z Sunday. Weakening is expected thereafter as Muifa crosses the cold-water plume to the east of Taiwan left behind by category 5 Super Typhoon Hinnamnor. Thereafter, Muifa is expected to slow down and enter a region of weak steering currents, which gives the long-term forecast higher uncertainty than usual. The storm’s very slow motion will upwell cool water, causing additional weakening, as will the higher wind shear predicted as Muifa approaches China. (Update: As of 8 a.m. EDT Sunday, Muifa’s top winds had reached 120 mph, and JTWC now expects this to be Muifa’s peak, with slow weakening thereafter. Muifa is predicted to be a 65-mph tropical storm near Shanghai on Thursday local time. A new system, Tropical Storm 15, is predicted to peak at category 1 strength in the open Northwest Pacific around midweek.)

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

Jeff Masters

Jeff Masters, Ph.D., worked as a hurricane scientist with the NOAA Hurricane Hunters from 1986-1990. After a near-fatal flight into category 5 Hurricane Hugo, he left the Hurricane Hunters to pursue a...