Just days after San Diego had the closest encounter with a hurricane of any U.S. city so far in 2022, Alaska ­- that’s right, Alaska – will be the next state to experience repercussions from a hurricane-strength storm. Multiple other tropical cyclones are a concern this week, including newly designated Tropical Depression Seven heading for the Antilles. Update: At 9:45 p.m. EDT Wednesday, TD 7 was upgraded to Tropical Storm Fiona, with top sustained winds of 50 mph.

Typhoon Muifa hits Shanghai area

Typhoon Muifa affected the world’s third most populous city, Shanghai, and its 25 million residents with an unusual direct landfall on Wednesday night local time. Muifa made its initial landfall in Putuo on Zhoushan Island, China (about 50 miles south-southeast of Shanghai), at 20:30 Beijing time (10:30 a.m. EDT). The storm quickly moved off the island and headed toward a second landfall on the north side of Hangzhou Bay (the south side of Shanghai’s urban core), becoming the strongest typhoon to reach the Shanghai area in records dating back to the establishment of the People’s Republic of China in 1949.

At its Zhoushan Island landfall, the Joint Typhoon Warning Center (JTWC) rated Muifa as a category 1 storm with 90 mph winds (1-minute average). JMA rated Muifa as having 90 mph winds (10-minute average), which implies slightly stronger winds on the 1-minute scale used by JTWC and the National Hurricane Center. Millions were evacuated ahead of Muifa in Zhejiang province, according to CGTN.

A minimum pressure of 963.4 mb was measured at Putuo Meteorological Station on Zhoushan Island as Muifa passed, with sustained winds of 80 mph, gusting to 113 mph. A 10-minute average wind of 41 meters per second (91.7 mph) was reported at Dongting Meteorological Station, near Zhoushan.

Figure 1. Radar image of Muifa at 12:54 a.m. local time September 15, when the center of Muifa was passing over Shanghai as a category 1 typhoon. At 12:30 am local time, Shanghai Pudong International Airport recorded sustained winds of 54 mph, gusting to 69 mph. (Image credit: CMA)

As it neared Shanghai, Muifa was packing gale-force winds over a swath more than 250 miles wide, with 57-mph sustained winds across a 130-mile-wide track. Widespread power outages and tree damage have likely occurred across this intensely populated region. The port cities of Ningbo and Zhoushan – together the second busiest in China – were closed on Wednesday as Muifa approached, according to CNN. At 2 p.m. EDT Wednesday, Muifa was still packing sustained winds of 80 mph, according to JTWC, and was located on the north side of Shanghai. Muifa is expected gradually weaken as it heads north along the coast of China over the next two days, and move inland north of North Korea on Friday.

Even though Shanghai is located in a typhoon-prone part of the world, it rarely experiences a direct landfall because the coastline angles northeast and then bends back north-northwest near the city and Hangzhou Bay, so a typical typhoon recurving to the northeast would bypass the area. It’s somewhat akin to the coastal geography that limits direct landfalls in southeast Virginia.

Fewer than a dozen typhoons have been recorded within 100 miles of Shanghai, none moving directly over the city as Muifa did. The most recent was Khanun in 2005, which inflicted more than $1.2 billion in damage (2005 USD) and took 16 lives on a rare northwestward track roughly similar to Muifa’s but further inland. In 1997, Typhoon Winnie stayed more than 200 miles south and west of Shanghai, yet the former category 5 typhoon came ashore as a sprawling category 1 storm with an expansive wind field and torrential rain. Damage in China from Winnie exceeded $3 billion US, and at least 300 people were killed, mainly through widespread flooding. Storm surge reached 6.57 meters (21.6 feet) at Jinshanzui in south Shanghai, according to a new analysis of surge cases and surge potential in the area.

Tropical Depression 7 a heavy rain threat to Leeward Islands and beyond

Tropical Depression Seven (TD 7) formed at 11 a.m. EDT about 800 miles east of the Leeward Islands, and it will be a heavy rain threat to those islands beginning on Friday. TD 7 took advantage of a small area of favorable conditions for development – a narrow region of mid-level moisture sandwiched by a large area of dry air that surrounds the depression on three sides (see Tweet below). Sea surface temperatures (SSTs) were warm, about 28.5 degrees Celsius (83°F) – about 0.5 degree Celsius (0.9°F) above average for this time of year. The first hurricane hunter mission into TD 7 is scheduled for Thursday afternoon.

Satellite images on Wednesday afternoon and evening showed that TD 7’s circulation center was nearly exposed to view, with the storm’s heavy thunderstorms restricted to the east side of the center because of strong upper-level winds out of the west that were creating a moderate 10-20 knots of wind shear.

Figure 2. Track forecasts out to 10 days for TD 7 from the 12Z Wednesday, September 14, run of the European ensemble model. Individual forecasts of the 51 ensemble members are the lines color-coded by the wind speed in knots they predict for TD 7; red colors correspond to a category 1 hurricane. The heavy black line is the ensemble mean forecast. The time in hours from the model initialization time are in black text. The more southerly ensemble members predicted that TD 7 would remain weak; the more northerly tracks showed a stronger system. (Image credit: weathernerds.org)

Forecast for TD 7

TD 7 is predicted to have marginal conditions for strengthening through early next week, when persistent moderate wind shear of 10-20 knots is expected to drive dry air into the core of the system. If TD 7 remains weak, the system will track faster and more to the south, bringing it through the Leeward Islands on Friday, the Virgin Islands and Puerto Rico on Saturday, and Hispaniola on Sunday. If the depression manages to overachieve and close off its core from the dry air surrounding it, a slower and more northward track is likely to result for the stronger storm. The system could potentially enter the Bahamas early next week, and an eventual threat to the U.S. East Coast later in the week is possible. The long-range forecast is complicated by a typhoon in the Pacific – Typhoon Merbok (see below) – which will merge with the jet stream late this week, potentially perturbing it significantly. That interaction is impossible to predict with much accuracy this far in advance. Update: In its 11 p.m. EDT Wednesday advisory, NHC predicted that newly named Tropical Storm Fiona will build top sustained winds of 60 mph on Thursday and maintain that strength through Monday, though some variation can be expected based on interactions with the islands. Tropical storm watches have been hoisted for some of the northern Leeward Islands.

Speedy shift ahead: from typhoon to major Alaska storm in just two days

Typhoon Merbok – which developed well to the northeast of the usual Northwest Pacific stomping grounds for typhoons – is predicted to evolve into a powerful post-tropical cyclone on Thursday, just a few hours before it reaches the Aleutian Islands and less than 48 hours before it slams Alaska’s west coast on Friday and Saturday. At 2 p.m. EDT Wednesday, Merbok was a category 1 typhoon with top sustained winds of 75 mph, moving north at 23 mph, according to the Joint Typhoon Warning Center (JTWC).

Figure 3. GEFS ensemble forecasts for Typhoon Merbok as it moves into the Bering Sea while transforming into a post-tropical cyclone. (Image credit: weathernerds.org)

Storms often rage in the Bering Sea in early autumn, but the post-tropical version of Merbok may go far beyond the usual into the truly dangerous. Forecasters are already warning of the potential for 50-foot-high waves.

The National Weather Service office in Anchorage is predicting wind gusts of up to 75 mph in coastal parts of southwest Alaska and up to 85 mph in the Aleutians, with 60-mph gusts possible as far inland as Bethel.

Nome, Alaska, could experience one of its largest storm surges in recent decades, perhaps topping the 8.73-foot surge in a destructive Bering Sea storm in November 2011 and not far from the 13-foot surge observed in a sequence of major storms in November 1974. With post-tropical Merbok arriving much earlier in the season than those two storms did, there will be little or no sea ice protecting the Bering Sea coast.

Figure 4. NOAA is predicting a storm surge near 10 feet on Saturday in Nome, Alaska.

Exceptional warmth across the Northern Hemisphere this summer (see today’s global climate roundup post) has led to unusually high sea-surface temperatures (SSTs) in many mid-latitude areas, including the North Atlantic as well as the Northwest Pacific. En route to Alaska, Merbok will traverse waters 2-3 degrees Celsius (3.6-5.4°F) warmer than average, helping fuel its intensity. An upper-level jet will provide favorable outflow for Merbok even as it becomes post-tropical. 

Taking a cue from Danielle and Earl in the Atlantic, Merbok reached its peak intensity at 8 a.m. EDT Wednesday well north of the tropics – in this case near 32 degrees north latitude. JTWC predicts Merbok will pack sustained winds of 70 mph on Thursday afternoon as it approaches the western Aleutian Islands while losing the last of its tropical characteristics.

As Merbok moves into high latitudes, it will help force jet-stream reverberations well downstream, helping to intensify an upper-level low near or off the U.S. West Coast early next week. In turn, a unusually strong upper ridge will lead to record or near-record heat over the central and eastern United States, perhaps affecting the future of Tropical Depression Seven (see above).

A new typhoon threat for Japan: Nanmadol

It’s a typically busy mid-September for the northwest Pacific, where a third named storm is active: Tropical Storm Nanmadol is a threat to develop into a major typhoon that will affect southern Japan this weekend. At 2 p.m. EDT Wednesday, the Joint Typhoon Warning Center (JTWC) pegged Nanmadol’s top winds at 60 mph (1-minute average), moving west at 6 mph. The Japan Meteorological Agency put Nanmadol’s intensity at 60 mph (10-minute average sustained winds).

Nanmadol had favorable conditions for intensification, with sea surface temperatures of 29-30 degrees Celsius (84-86°F), light wind shear of 5-10 knots, and a moist atmosphere. The Joint Typhoon Warning Center’s 5 p.m. EDT Wednesday advisory called for a period of steady intensification to begin on Wednesday night (U.S. EDT), with Nanmadol topping out as a major typhoon with 120 mph winds at 18Z Saturday. Weakening is expected thereafter as the typhoon interacts with the landmass of southern Japan, before an expected Sunday landfall as a borderline category 1 or 2 typhoon.

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Bob Henson

Bob Henson is a meteorologist and journalist based in Boulder, Colorado. He has written on weather and climate for the National Center for Atmospheric Research, Weather Underground, and many freelance...

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...