Bob Henson ·

Above: GOES-16 view of Hurricane Jose, Tropical Storm Maria, and Tropical Depression Lee at 10:45 am EDT September 17, 2017 . Image credit: NOAA/RAMMB. GOES-16 data is considered preliminary and non-operational.

The islands of the northeast Caribbean hard-hit by Hurricane Irma are bracing for the impact of another ferocious Cape Verde-type hurricane, as Tropical Storm Maria, packing winds of 65 mph, headed west-northwest at 15 mph late Sunday morning. Hurricane watches were up for all of the Lesser Antilles Islands blasted by Irma’s eyewall winds earlier this month, including Barbuda, St. Maarten/St. Martin and St. Barthelemy, and Anguilla. Hurricane watches and tropical storm watches extended southwards to encompass nearly the entire Lesser Antilles chain of islands, and a Hurricane Warning was posted for Dominica. Maria is likely to be a Category 2 or Category 3 hurricane when it passes through the Lesser Antilles Islands on Monday night and Tuesday morning.

Maria had very favorable conditions for development on Sunday. Wind shear was light, 5 - 10 knots, SSTs were a very warm 29 – 29.5°C (84 - 85°F), and relative humidity at mid-levels of the atmosphere (as analyzed by the 12Z Sunday run of the SHIPS model) was moderately moist--about 60%. Satellite loops showed that Maria was developing an impressive area of heavy thunderstorms that were increasing in areal coverage and intensity, with low-level spiral bands and a respectable upper-level outflow channel forming. However, a tendril of dry air had wrapped into the west side of Maria’s circulation late Sunday morning, arresting Maria’s intensification process. The first hurricane hunter aircraft is scheduled to investigate Maria on Sunday afternoon, which will tell us more about Maria’s structure and strength.

Figure 1. The 20 track forecasts for Maria from the 0Z Sunday, September 17, 2017 GFS model ensemble forecast. Image credit: CFAN.

Figure 2. The 50 track forecasts for Maria from the 0Z Sunday, September 17, 2017 European model ensemble forecast. The operational European model is the red line, adjusted by CFAN using a proprietary technique that accounts for storm movement since 0Z Sunday. The track of the average of the 50 members of the European model ensemble is the heavy black line. There is a lot of uncertainty in the long-range fate of Maria. Image credit: CFAN.

Track forecast for Maria

The ridge of high pressure steering Maria will weaken on Monday and Tuesday, which will force the storm to slow; Sunday morning’s forward speed of 15 mph will decrease to about 8 mph from Monday morning through Tuesday afternoon. A continued west-northwest motion is expected to occur, though, bringing the core of the intensifying storm into the northern Lesser Antilles Islands on Monday night and Tuesday morning. Our most reliable track model, the European, had the most southerly track for Maria in its Sunday morning forecast, as did NHC (and the 12Z run of the GFS), predicting that the center of Maria would pass over Guadeloupe. Our other reliable models—the GFS, UKMET, HWRF, and HMON—predicted a slightly more northerly track, resulting in a direct hit on Montserrat and Antigua. By Tuesday afternoon, Maria will be pounding the U.S. and British Virgin Islands, which were also devastated by Irma. Maria will pass very close to Puerto Rico on Wednesday, and the Dominican Republic on Thursday.

Beyond Thursday, the path of Maria will largely depend upon what Hurricane Jose is up to. If Jose is still wandering off the U.S. New England coast, this may help create a weakness in the ridge of high pressure steering Maria, giving Maria a chance to gradually recurve and avoid the U.S. East Coast. If Jose is out of the picture, or if the ridge rebuilds south of it, this would tend to keep Maria heading west-northwest, which could pose a threat the U.S. East Coast more than a week from now. In either case, Maria is likely to be a threat to the southeast Bahamas and Turks and Caicos Islands toward the end of this week and into the weekend.

Intensity forecast for Maria

The 12Z Sunday run of the SHIPS model predicted that Maria would have very favorable conditions for development over the next five days. The atmosphere will be moist, wind shear will be quite low (generally less than 10 knots), SSTs will be a very warm 29.5°C (85°F), and ocean heat content will be high, around 70 kilojoules per square centimeter—only slightly less than what Hurricane Irma had to work with when it exploded into a high-end Category 5 hurricane about two weeks ago. These conditions should allow for strengthening of Maria, and a period of rapid intensification is likely at some point over the next three days. On Sunday morning, two of our top intensity models—the HWRF and COAMPS-TC—predicted that Maria would be a Category 3 hurricane by Tuesday morning, when the storm is expected to be moving through the Lesser Antilles. The other top intensity models—DSHIPS, LGEM, and HMON—were more restrained, predicting a Category 1 or 2 hurricane then. Given the favorable atmospheric and oceanic conditions, Maria will likely be a Category 2 or 3 hurricane on Tuesday morning in the Lesser Antilles.

There is nothing obvious in Maria’s environment to prevent strengthening through Wednesday afternoon, when interaction with Puerto Rico and/or Hispaniola may disrupt the storm. Both the HWRF and COAMPS-TC models predicted in their Sunday morning runs that Maria would be a Category 4 hurricane on Wednesday afternoon, and Maria will most likely be at Category 3 or 4 strength when making its closest approach to Puerto Rico on Wednesday. The Rapid Intensification Index from the 12Z Sunday SHIPS model run gave Maria a 42% chance of gaining 65 knots of intensity over the next three days, which would bring Maria to the threshold of Category 4 strength by Wednesday.

Figure 3. Infrared image of Hurricane Jose as of 11 am EDT Sunday, September 17, 2017. Image credit: NASA/MSFC Earth Science Branch.

Jose to skirt the U.S. coast—then what?

The future track of Maria will depend in part on how Hurricane Jose evolves off the U.S. East Coast. Located about 350 miles southeast of Cape Hatteras at 11 am EDT Sunday, Jose was hanging in as a Category 1 hurricane. Although Jose’s top winds were increased from 80 to 90 mph based on Hurricane Hunter data from Sunday morning, the hurricane showed no signs of major strengthening on satellite. Jose has put up an impressive battle, though, maintaining a core of strong thunderstorms against fierce wind shear of 25 - 35 knots.

Jose will be moving north over the next couple of days, bringing it to within about 200-300 miles of the Outer Banks of North Carolina by late Monday. Tropical-storm-force winds are predicted to extend no more than 200 miles to the west of Jose’s center, so the main impact on the Outer Banks will be high surf (up to 16 feet) and rip currents. Jose’s outer fringe could bring the area a few squally showers. Bermuda and The Bahamas will also continue to be pounded by rough surf from Jose.

From Tuesday into Wednesday, Jose is expected to arc northeast on a path that will gradually bring it closer to the U.S. coast, with high surf and rip currents increasing northward to New England. Tropical-storm-force winds could nudge into southeast New England by this point: NHC gives Nantucket a 35% chance of tropical-storm-force winds on Tuesday, with a 30% chance at Montauk, New York, on the eastern tip of Long Island. Minor to moderate coastal flooding will be possible, and several inches of rain could drench southeast New England, with a sharp cutoff on the northwest side of the heavy rain.

From midweek onward, there is major disagreement among our top track models on Jose’s future. This track uncertainty hinges in part on fast-moving, difficult-to-resolve features in the jet stream rolling across the northern U.S. and southern Canada and into the North Atlantic. In their 00Z Sunday runs, the European and UKMET models predicted that Jose will carry out a cyclonic loop roughly 100-200 miles south of Long Island, New York. The UKMET had a tighter loop, with Jose moving west to the New Jersey coast by Friday. The Euro model kept the offshore loop going into at least next weekend, with an eventual southward dip into the North Carolina coast. Meanwhile, the GFS and HWRF models kept Jose further east, on a much broader and more leisurely loop that has the storm north of Bermuda by next weekend. The official NHC track forecast is much more in line with the eastward GFS and HWRF tracks than with the European and UKMET solutions. A more eastward track would also leave a weakness that could help steer Maria away from the U.S. East Coast.

Figure 4. The 0Z Sunday September 17, 2017, track forecast by the operational European model for Jose (red line, adjusted by CFAN using a proprietary technique that accounts for storm movement since 0Z Thursday), along with the tracks of the 5 highest-probability members of the European model ensemble (gray lines), and the mean track forecast from all 50 members of the ensemble (black line). Note that even the 5 highest-probability members are in stark disagreement beyond 3-4 days, with landfalls ranging from North Carolina to Nova Scotia. Image credit: CFAN.

Figure 5. The 20 track forecasts for Jose from the 0Z Sunday, September 7, 2017 GFS model ensemble forecast. Only 2 of the 20 tracks predict an eventual U.S. landfall, and most of the ensemble is consistent in taking Jose well east of the U.S. coast. However, just because the GFS ensemble is more unified than the Euro ensemble doesn’t necessarily mean it’s correct! The Euro may be picking up on bona fide uncertainty in the steering patterns that cannot be resolved at this point. Image credit: CFAN.

Jose likely to become a sprawling gale and surf generator

No matter which model has the best handle on its track, Jose will probably evolve into a much different creature than it is now. Vertical wind shear will be relentless through Tuesday, capping Jose’s strength. Beyond Tuesday, Jose will be moving over SSTs below 26°C (79°F), which is too cool to support tropical development. This means Jose will begin to take on characteristics of a midlatitude (post-tropical) storm as the week progresses. A post-tropical Jose would have a weaker core wind field but a larger zone of gale-force winds, so coastlines from North Carolina to southern New England are in for a long period of rough surf and an increasing risk of beach erosion. If Jose were to make landfall, it could end up producing significant surge even as a post-tropical storm.

Tropical Depression Lee on its last legs

At least one of our three named Atlantic systems won’t be causing any trouble. Tropical Depression Lee was downgraded from tropical-storm status at 11 am EDT Sunday, after having achieved only minimal tropical storm strength. Located in the remote eastern tropical Atlantic, about 900 miles southwest of the Cabo Verde Islands, Lee was moving west at 8 mph. ASCAT scatterometer data showed that top winds were only 35 mph, mainly to the east of Lee’s center, and only a few weak thunderstorms were scattered across Lee’s circulation. NHC predicts that Lee will degenerate into a remnant low by Tuesday, if not sooner.

Figure 6. Infrared satellite image of Tropical Storm Otis (left) and TS Norma (right) at 11:45 am EDT Sunday, September 17, 2017. Image credit: NASA/MSFC Earth Science Branch.

Less-than-impressive TS Norma lingers off Baja California

Tropical Storm Norma failed to live up to its potential in the East Pacific, and that’s good news for Baja California. Formerly a Cat 1 hurricane, Norma moved over a shallow surface layer of water just warm enough to sustain tropical development. However, Norma’s lackadaisical pace allowed it to churn up cooler water, which dented its growth. Dry air wrapping into Norma from the south also took a toll on the storm. As of 11 am EDT Sunday, Norma was a weakening tropical storm with top winds of just 45 mph, located about 145 miles south-southwest of Cabo San Lucas, Mexico. A tropical storm watch remained in effect for the southernmost Baja Peninsula, but since Norma is moving north-northwest at just 5 mph, it’s very possible that dry air will finish off Norma before it can bring tropical storm conditions to the coast. NHC predicts Norma to be a depression by Monday night and a remnant low by Wednesday, still drifting about 100-200 miles west of Baja California.

A new East Pacific system, Tropical Storm Otis, is located about 1200 miles west-southwest of Baja California, with top winds up to 60 mph as of 11 am EDT Sunday. Otis may briefly hit hurricane strength before weakening later this week, posing no threat to land.

There are no other systems of interest in the Atlantic or East Pacific. In the Northwest Pacific, a former typhoon, Tropical Storm Talim, was sweeping across central Japan late Sunday with gale-force winds and heavy rain. Talim’s rapid northeast motion should cut down on the threat of flooding and mudslides, according to weather.com.

Jeff Masters co-wrote this post.