Tropical Storm Nicholas, which formed Sunday morning in the southwest Gulf of Mexico, is on track to make landfall by Monday evening in Texas as a strong tropical storm or low-end category 1 hurricane. Slow-moving Nicholas will be a dangerous flood threat for much of coastal Texas and Louisiana. Nicholas will be the eighth named storm to strike the continental U.S. so far in 2021.

Figure 1. Infrared image Tropical Storm Nicholas at 12:16 p.m. EDT Monday, September 13, 2021. (Image credit: NOAA)

At 11 a.m. EDT Monday, the newly-reformed center of Nicholas was about 140 miles south of Port O’Connor, Texas. Nicholas was moving north at roughly 12 mph with top sustained winds of 60 mph, bringing heavy rains to most of the central Texas coast. Onshore winds blowing along the central Texas coast were bringing a storm surge of 1-1.5 feet at 1 p.m. EDT Monday, according to NOAA Tides and Currents.

Radar imagery showed Nicholas attempting to form a new center near the storm’s heaviest thunderstorms, about 100 miles north of the old center, and Nicholas has been struggling to maintain a well-defined center. Strong upper-level winds were creating moderate to high wind shear of 15-20 knots, but the upper-level winds were nearly aligned with the storm’s motion, thus helping to provide upper-level outflow and reduce the impact of the shear on Nicholas. Conditions were otherwise favorable for intensification, with warm ocean waters of 30 degrees Celsius (86°F) and a moist atmosphere with mid-level relative humidity of 65%.

Forecast for Nicholas

Forecast models are consistent in bringing Nicholas northward until landfall by Monday evening over the central Texas coast. After landfall, Nicholas will turn more to the northeast and slow down to a forward speed of 7-10 mph, allowing the storm to keep some of its circulation over water and generate heavy rains for multiple days. With widespread rains of 8-16 inches predicted through Wednesday over much of coastal Texas and Louisiana, damaging floods costing hundreds of millions of dollars are likely.

Storm surge from Nicholas will also be capable of causing damaging moderate flooding along the coast. The National Hurricane Center is predicting a 3- to 5-foot surge over much of the central Texas coast, and two to four feet in Galveston Bay. This storm surge will impede flood waters from Nicholas’ heavy rains from draining into the ocean, compounding the coastal flood threat.

Tropical storm-force winds capable of bringing down trees and power lines will occur with Nicholas as it moves inland. A few tornadoes can also be expected along the central Texas coast on Monday; NOAA’s Storm Prediction Center has said this region is in its “Slight Risk” area for severe weather.

Figure 2. Visible image of a large area of disturbed weather north of Hispaniola and east of the Southeast U.S. at 1520Z (11:20 a.m. EDT) Monday, September 13, 2021. (Image credit: RAMMB/CIRA/CSU)

Future of potential Bahamas system: highly uncertain

Computer models continue to suggest that an upper-level low north of Hispaniola, a surface front to its north, and a tropical wave approaching from the east may join forces to produce a surface low by midweek northwest of the Bahamas.

Steering currents would most likely take this amorphous system gradually northwest toward the U.S. Mid-Atlantic coast, but it is far from clear whether there will be any U.S. impacts. Only a couple of 0Z Monday European model ensemble members indicated tropical development from this low, and only a small minority of GFS ensemble members brought the system to tropical storm strength. The 0Z Monday runs of the GFS, Euro, and UKMET long-range models all show a weak low that remains offshore, roaming the territory between the East Coast and Bermuda for a few days.

It is possible that the moisture channel streaming northeast from Nicholas will interact with the developing low, but most of the rainfall with the low is now projected to remain offshore, though the North Carolina Outer Banks could receive heavy rains from the system beginning on Thursday morning.

In its 2 p.m. EDT Monday Tropical Weather Outlook, the NHC gave this system 2-day and 5-day odds of development of 10% and 50%, respectively. Should development occur, the most likely scenario is a tropical depression or a weak tropical storm well off the U.S. East Coast through at least this coming weekend. By early next week, a strong upper-level ridge building over the Northeast could keep any lingering development from moving quickly out to sea, keeping the storm lingering off the coast. A hurricane hunter aircraft is scheduled to investigate the system on Wednesday.

Figure 3. MODIS visible satellite image of 95L along the coast of Africa on Monday morning, September 13, 2021. (Image credit: NASA Worldview)

Disturbance 95L near Africa definitely one to watch

The NHC has designated a tropical wave that moved off the coast of Africa on Monday morning as 95L. This wave has strong model support for development, and the potential to develop into a long-track Cape Verde-type hurricane by this weekend as it heads west to west-northwest at 10-15 mph.

95L will have favorable conditions for development this week, with warm sea surface temperatures of 27-28 degrees Celsius (81-82°F), mostly moderate wind shear of 10-20 knots, and a moist atmosphere with a mid-level relative humidity of 65-80%. However, 95L is expected to face a major obstacle to further intensification early next week, when it approaches the Leeward Islands: a large upper-level trough of low pressure. This trough is predicted to have high wind shear and dry air, and most model forecasts have 95L weakening significantly or being destroyed by the trough by early next week.

There is much uncertainty with forecasts this far in advance, and the danger 95L might pose to the Caribbean islands or North America remains to be seen. In its 2 p.m. EDT Monday Tropical Weather Outlook, the NHC gave 95L 2-day and 5-day odds of development of 30% and 80%, respectively. The next name on the Atlantic list of storms is Odette.

Chanthu weakens, pulls its punch against Shanghai

After sparing Taiwan a direct hit, former category 5 Typhoon Chanthu is also sparing Shanghai the heavy rains that were initially feared. Chanthu is now tracking farther offshore than predicted, keeping its heaviest rains just offshore from China’s largest city.

At 11 a.m. EDT Monday, slow-moving Chanthu was a category 1 typhoon with 75 mph winds located 110 miles east of Shanghai and moving north at just 3 mph. Chanthu was bringing heavy rains to Shanghai, as seen on Chinese radar, but total rainfall from the storm in the city should remain less than five inches, sparing the city major flood damage. Shanghai has already suffered damaging flooding from one other slow-moving typhoon this year: Typhoon In-fa caused $1.1 billion in damage July 22-26, dumping 37.4 inches of rain at Dalan Town, China.

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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...

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...