The Northern Hemisphere tropics are churning along at a classic peak-season pace, with two landfalls on Friday evening U.S. time that were distinctive in different ways. Two Atlantic systems are likely to become tropical depressions, if not named storms, by early next week, and development is also possible later next week just off the U.S. East Coast and off the coast of Africa.

The next two names on the Atlantic list are Nicholas and Odette, both used only once before, for tropical storms in 2003.

Larry strikes Newfoundland

Hurricane Larry made landfall in southeastern Newfoundland, Canada as a category 1 storm with 80 mph winds and a central pressure of 960 mb at 11:45 p.m. EDT September 10, 2021. Shortly after landfall, the core of the hurricane passed over Newfoundland’s capital, St. Johns, which recorded sustained winds of 60 mph, gusting to 90 mph. A peak gust of 113 mph was reported at Cape St. Mary’s lighthouse, according to CBC meteorologist Ryan Snoddon. CBC also noted a storm surge of 4.9 feet at Argentia on the west-facing shore of the Avalon Peninsula in western Newfoundland.

Power was knocked out for some 60,000 Newfoundlanders at the storm’s peak.

Figure 1. Radar image of Hurricane Larry at 11:05 p.m. EDT September 10, 2021, about 40 minutes prior to landfall.

Hurricanes hit Newfoundland every decade or two on average. Larry was the first to strike the island since Hurricane Igor of 2010, and the fourteenth in records going back to 1851. Larry’s long tenure as an annular hurricane – a type that tends to resist weakening – helped it to retain hurricane strength all the way to latitude 50.7°N at 5 a.m. EDT Saturday, before being declared post-tropical at 11 a.m. (by that point, it was at latitude 54.0°N).

Only a handful of hurricanes in the satellite era have made it north of latitude 50° before going post-tropical. The most recent were Debby (1982), which reached latitude 50.8°N as a hurricane, and Helene (1988), which made it to 50.2°N.

As Larry continues northward, it will evolve into a potent snowmaker. The GFS model is calling for Larry to dump around 20 gigatonnes of snow in three days across southeast Greenland. That would be roughly 3% of a typical year’s worth of snow for the entire Greenland ice sheet, based on 1981-2010 data.

Figure 2. Infrared satellite image of Chanthu at 1530Z (11:30 a.m. EDT) Saturday, September 11, 2021, with Chantu’s track to date and projected track with Saffir-Simpson categories overlaid. (Image credit: CIMSS/SSEC/UW-Madison)

Chanthu makes a rare Cat 5 landfall

Landfalls by category 5 tropical cyclones are rare, since these storms are thankfully so few in number. No country on Earth sees more category 5 landfalls than the Philippines, though, which lies next to the largest area of deep warm waters anywhere on the planet. On Friday evening, the Philippines added another Cat 5 landfall to its history books: The eye of Chanthu passed directly over the municipality of Ivana on Philippines’ Batan Island (population 13,000) at 0Z Saturday, September 11. At the time, Chanthu was a category 5 storm with 165 mph winds (see Tweet below, and note that the Philippines calls Chanthu by the name Kiko).

Earth’s most recent Cat 5 landfall before Chanthu occurred just last year: On November 1, 2020, Super Typhoon Goni hit the Philippines’ Catanduanes Island with 195 mph sustained winds, making it the strongest landfalling tropical cyclone in world recorded history.

Chanthu will pass just east of Taiwan this weekend, keeping the island on its weaker left-hand side. Still packing top winds of 140 mph as of 15Z Saturday, Chanthu will gradually weaken as it continues northward toward cooler waters and drier air. Still, torrential rains and mudslides will be a major threat in central and eastern Taiwan, with widespread 3-to-10-inch rainfall totals at higher elevations.

By early next week, Chanthu is predicted to slow as it approaches Shanghai as a category-1-equivalent typhoon before taking a sharp right turn offshore.

Figure 3. Infrared satellite image of disturbance 94L as of 1540Z (11:40 a.m. EDT) Saturday, September 11, 2021. (Image credit: RAMMB/CIRA/CSU)

A wet week ahead for coastal areas of Texas and Louisiana as disturbance 94L looms

A tropical disturbance named 94L could become a troublesome rainmaker next week along the Texas and Louisiana coasts. At midday Saturday, 94L was moving across southern Mexico as a poorly organized system, with only scattered showers and thunderstorms (convection) well away from its center.

94L is expected to move offshore into the Bay of Campeche later this weekend, then move slowly northward across the western Gulf of Mexico toward Texas early next week. Wind shear will remain a high 15-25 knots throughout the period, and as strongly suggested by the European and GFS model ensembles, the shear and 94L’s proximity to land will likely hinder any dramatic tropical development. However, some modest strengthening of 94L can be expected, given the very moist atmosphere around 94L (mid-level relative humidity around 80 percent) and the very warm sea surface temperatures (SSTs) it will traverse (around 29 degrees Celsius or 84°F). Assuming it does develop, 94L will likely be a “coast scraper” and will largely run parallel to the Mexico and Texas coasts prior to landfall. This track would keep the system’s strongest wind field on the offshore side. An Air Force reconnaissance flight into 94L is scheduled for Sunday.

In its tropical weather outlook issued at 2 p.m. EDT Saturday, the National Hurricane Center gave 94L an 80% chance of becoming at least a tropical depression by Monday and a 90% chance through Thursday.

Heavy rains will likely be the main threat from 94L. Even though its chances of becoming a hurricane are on the low side, especially if it hugs the Texas/Mexico coast as expected, 94L will be pushing a very moist air mass toward the Texas and Louisiana coastline. (See the blue areas in the tweeted graphic above, which depicts precipitable water, or the total amount of moisture in the atmosphere above a given point). A frontal system is likely to sharpen near the coast, further enhancing the potential for heavy rain.

Rainfall through next week could total 7 to 10 inches over much of the immediate coastal region, with localized total of 10 to 15 inches (or even higher) quite possible.

Figure 4. 7-day rainfall forecast from 8 a.m. Saturday, September 11, 2021, to Saturday, September 18. Specifics of timing and location will vary depending on the track of 94L. (Image credit: NOAA/NWS Weather Prediction Center).

Disturbance 93L is the next Eastern Atlantic system to watch

Tropical disturbance 93L is on track to bring squally conditions to the Cabo Verde Islands as it moves across the archipelago this weekend. Though it has only weak convection, 93L is a well-structured system and on Saturday afternoon appeared to be developing a low-level circulation. Wind shear will be light to moderate (5-10 knots) through Sunday, and SSTs of around 27 degrees Celsius (81°F) will support gradual development. NHC gives 93L a 50% chance of becoming at least a tropical depression by Monday and a 70% chance by Thursday.

As it heads mainly westward close to latitude 15°N, 93L will encounter intensifying wind shear, especially by midweek, and it will not reach dramatically warmer water over this period. Even if it does develop, the most likely outcome is that 93L will weaken later next week, as suggested by most of the European and GFS ensemble model members.

Figure 5. Infrared satellite image of disturbance 93L as of 1330Z (9:30 a.m. EDT) Saturday, September 11, 2021. (Image credit: RAMMB/CIRA/CSU)

Two other systems are on the Atlantic’s long-range horizon

Another system to watch is already evident as a strong easterly wave over Africa. This wave is likely to emerge into the eastern Atlantic tropics early next week at a lower latitude than 93L, which will give it a better chance of long-term strengthening. NHC gives this new system a 20 percent chance of development between Tuesday and Friday.

Near the southeastern Bahamas, yet another disturbance may take shape next week. If so, it will most likely be heading toward the U.S. East Coast. Multiple long-range runs of the GFS model have shown a developing system reaching the mid-Atlantic toward the end of next week, although the European model has been less emphatic. NHC gives this potential system a 20 percent chance of development between Tuesday and Friday.

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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, 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...