Jeff Masters Weather Blog

Ophelia drenches the U.S. East Coast » Yale Climate Connections

Rains from Tropical Storm Ophelia swept northward from Virginia into New England on Sunday, topping off a soggy weekend along the Interstate 95 corridor from Washington, D.C., to Boston. The heaviest totals from Sunday into early Monday, in the 3-to-5-inch range, stretched from northeast Pennsylvania across the lower Hudson Valley of New York into Connecticut. Peak 24-hour totals through Monday morning included 4.05 inches near Hawley, PA; 3.70 inches at Ulster Park, NY; and 3.60 inches at Salisbury, CT.

Some of Ophelia’s worst flooding occurred just inland from the Atlantic coast in eastern North Carolina, where runoff from heavy rains collided with storm surge pushing upriver. Extensive downtown flooding was reported in low-lying parts of New Bern and Washington, NC. Along the Atlantic coast, Ophelia’s storm surge was generally a half-foot to a foot below predictions, which limited coastal flooding.

Wind shear keeping Philippe in check for now

Tropical Storm Philippe is hanging on over the central tropical Atlantic, almost 1200 miles east of the northern Leeward Islands, but Philippe is currently in maintenance mode at best. Strong wind shear of 15-20 knots has kept the storm from consolidating and intensifying despite warm sea surface temperatures around 29 degrees Celsius (84 degrees Fahrenheit) and a moist mid-level atmosphere (relative humidity 60-65 percent). The westerly wind shear has shoved Philippe’s extensive field of convection (showers and thunderstorms) completely east of the storm’s low-level center, as shown in Figure 1 below.

A satellite image of clouds rotating over the ocean.
Figure 1. Satellite image of Tropical Storm Philippe at 1710Z (1:10 p.m. EDT) Monday, September 25, 2023. (Image credit: RAMMB/CIRA/CSU)

At 11 a.m. EDT Monday, Philippe was tracking just north of due west at about 13 mph. Top sustained winds were pegged at 50 mph. Over the next several days, wind shear is predicted to increase to the 20-30 knot range over the next several days, so despite even warmer sea surface temperatures near 30°C (86°F) along Philippe’s path, the already-asymmetric storm will be plagued by intrusions of dry air by midweek. Assuming Philippe can survive these less-than-ideal conditions, it will have a chance to intensify by late week, when wind shear is expected to ramp down. Splitting the difference somewhat, the National Hurricane Center on Monday predicted that Philippe would remain a 50-mph tropical storm all the way into Saturday.

Philippe is expected to angle slightly toward the west-northwest by midweek. Over the longer term, Philippe’s track will hinge on whether or not it intensifies, weakens, or holds steady: the stronger Philippe is, the more it will feel upper-level steering currents that would steer it clear of the Caribbean, while a weaker Philippe would be more driven by lower-level easterly winds that might push it toward the Greater Antilles. As the National Hurricane Center put it on Monday morning, there was a “vast amount of spread” in model projections of Philippe’s future. As of Sunday night (see Figure X), the GFS model kept a stronger Philippe heading more firmly northwest through the week, with all of the GFS ensemble members staying well away from the Caribbean islands. The National Hurricane Center was considering the GFS solution to be an outlier outcome. In contrast, the European and UKMET models and their ensembles were predicting a weaker Philippe to maintain or resume a west-northwest course, with a few ensemble members nudging within several hundred miles to Hispaniola, Puerto Rico, and the Virgin Islands. However, both the Euro and UKMET operational runs dissipate this weaker Philippe, as shown by the lack of large-dot endpoints on those two tracks in Figure 2.

Figure 2. Ensemble tracks for Philippe produced on Sunday night, September 24, extending out seven days. Also shown are the operational (deterministic) model tracks for the European (red), GFS (green), and UKMET (blue) models, and the mean track of all ensemble members (black). (Image credit: Tomer Burg)

Next Cabo Verde wave likely to develop later this week

A strong tropical wave emerged off the coast of western Africa over the weekend, and this wave appears likely to become our next named storm.  The disturbance, called Invest 91L, was located on Monday a few hundred miles southwest of the Cabo Verde Islands. Convection was scattered in disorganized fashion around 91L, and it will take time for the disturbance to organize. Conditions are similar to those that spawned Philippe: warm sea surface temperatures (around 29°C or 84°F) and a moist mid-level atmosphere (relative humidity around 70 percent), but moderate wind shear (10-15 knots) that will ramp up to 15-20 knots by midweek.

Figure 3. Satellite image of Invest 91L at 1615Z (12:15 p.m. EDT) Monday, September 25, 2023. (Image credit: RAMMB/CIRA/CSU)

91L will be moving west-northwest in Philippe’s oceanic footsteps, and long-range models suggest a good chance 91L will eventually recurve well east of North America, though it is way too soon to make any confident predictions. In its Tropical Weather Outlook issued at 2 p.m. EDT Monday, the National Hurricane Center gave 91L a 30 percent chance of becoming at least a tropical depression over the next two days, with seven-day odds of 80 percent.

Gulf disturbance not expected to develop

An area of unsettled weather was simmering over the southeast Gulf of Mexico and adjacent northwest Caribbean on Monday. Convection was bubbling across a broad area of rotation in conjunction with an upper-level low, but there was no sign of any low-level center trying to organize on Monday. As the upper low pulls northward, westerly wind shear – quite typical of autumn in the Gulf during El Niño – will increase across the area, further limiting any chances of organization. In its Tropical Weather Outlook issued at 2 p.m. EDT Monday, the National Hurricane Center gave the disturbance near-zero odds of development over the next two and seven days.

Jeff Masters 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.

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