Above: Radar image of Maria at 10:30 am EDT September 18, 2017, from the Barbados radar.
The Leeward Islands are enduring their second major hurricane in two weeks, as the outer spiral bands of rapidly intensifying Category 3 Hurricane Maria lash the islands. Rain squalls and rising winds were already being observed late Monday morning at Melville Hall Airport on Dominica, which measured sustained winds at 25 mph at 11 am EDT Monday. A wind gust of 32 mph was observed at Guadaloupe at 11 am. Satellite loops and radar out of Martinique and Barbados clearly showed Marie’s small, 12-mile diameter eye, surrounded by an impressive array of spiral bands with heavy thunderstorms, headed west-northwest at 10 mph towards Dominica. An Air Force hurricane hunter aircraft found that Maria’s hurricane-force winds were confined to a relatively narrow 30-mile diameter region around the hurricane’s small 12-mile diameter eye, but tropical storm-force winds extended out 125 miles from the center.
|Figure 1. The 20 track forecasts for Maria from the 0Z Monday, September 18, 2017 GFS model ensemble forecast. Most of the solutions show Maria missing the continental U.S. in the long range. Image credit: CFAN.|
|Figure 2. The 50 track forecasts for Maria from the 0Z Monday, September 18, 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 Monday. The track of the average of the 50 members of the European model ensemble is the heavy black line. Most of the solutions show Maria missing the continental U.S., but being a threat to Canada in the long-range. Image credit: CFAN.|
Track forecast for Maria
The ridge of high pressure steering Maria has weakened some, and the hurricane is expected to move west-northwest at about 10 mph for the next four days. On this track, the center of Maria will cross Dominica at approximately 8 pm EDT Monday, bringing the full fury of its eyewall winds to that island. The Dominica weather service is expecting waves of 10 – 12 feet to impact the island. Guadeloupe to the north may experience the powerful right-front eyewall winds, and Martinique to the south the weaker left front eyewall winds. The Leeward Islands devastated by Irma’s 185 mph winds two weeks ago—Barbuda, Anguilla, St. Barthelemy, Saint Martin, and Sint Maartin--are likely to miss extreme devastation by Maria’s eyewall winds, but will still receive dangerous flooding rains and damaging hurricane-force wind gusts. It’s too close to call right now whether or not the islands of Antigua, Montserrat, St. Kitts and Nevis, Sint Eustatius, and Saba will experience the destructive winds of Maria’s right-front eyewall yet.
The models are tightly clustered in their Tuesday and Wednesday track forecasts, bringing the center of Maria through the U.S. and British Virgin Islands or Puerto Rico on Tuesday night and Wednesday morning. Our most reliable track model, the European, had the most southerly track for Maria in its Monday morning forecast, as did NHC. Whereas Irma's track was close to the northern U.S. Virgin Islands (St. Thomas and St. John), Maria has the potential to move over or near St. Croix--the southernmost U.S. Virgin Island. Maria’s impact on the U.S. Virgin Islands and Puerto Rico may well make Maria the third Category 4 billion-dollar hurricane for the U.S. this year, in addition to Harvey and Irma. Maria will pass very close to the eastern Dominican Republic on Thursday, and the Turks and Caicos Islands on Friday.
Beyond Thursday, there is increased confidence that Maria will turn to the northwest and then north-northwest, staying well to the east of Florida, in response to a weakening of the ridge of high pressure steering the storm caused by Hurricane Jose to the north. The forecast for Jose is very complex, as the storm will be in an area of weak steering currents and will be undergoing transition to an extratropical storm (see discussion below in the Jose section.) This uncertainty in Jose’s future makes it much too early to judge what portions of the U.S. East Coast or Canada might be threatened by Maria next week.
Intensity forecast for Maria: Cat 4 likely, Cat 5 possible
Maria had very favorable conditions for development on Monday. 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 Monday run of the SHIPS model) was moist--about 65%. The 12Z Monday run of the SHIPS model predicted that Maria would continue to 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, between 60 – 80 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 continued strengthening of Maria, and 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. The Hurricane Hunters on Monday morning noted that Marie’s eyewall was open to the southwest, and the hurricane will have to close off this gap if it is to intensify into a 150 mph Category 4 storm--the official NHC intensity forecast.
On Monday morning, our three top dynamical intensity models—the HWRF, HMON, and COAMPS-TC—predicted that Maria would be a Category 4 hurricane on Tuesday and Wednesday. The other top intensity models—the statistical DSHIPS and LGEM—had lower intensity forecasts, but these models have been under-forecasting Maria’s intensity increases. Given the favorable atmospheric and oceanic conditions, Maria will likely be a Category 4 hurricane on Tuesday and Wednesday, and could become a Cat 5. The Rapid Intensification Index from the 12Z Monday SHIPS model run gave Maria a 49% chance of gaining 35 mph in intensity by 8 am Tuesday, which would make Maria a powerful Category 4 hurricane with 150 mph winds. The model also gave Maria a 34% chance of reaching Category 5 status on Tuesday, and projected that the maximum potential intensity that the hurricane could reach would be 180-mph winds.
Bottom line: Maria will likely be an extremely dangerous Category 4 hurricane when it affects the Virgin Islands and Puerto Rico on Tuesday night and Wednesday, and could be a catastrophic Category 5 storm.
|Figure 3. Tracks of Hurricane Jose and Hurricane Lenny of 1999, the last twin hurricanes to affect the Leeward Islands in the same year. Image credit: NOAA|
|Figure 4. Tracks of Hurricane Luis and Hurricane Marilyn of 1995. Image credit: NOAA.|
Irma and Maria: the first twin major hurricanes for the Leeward Islands since 1899
Maria’s strike on the Leeward Islands comes just two weeks after Category 5 Hurricane Irma ripped through, causing catastrophic damage. It is uncommon to have two hurricanes hit the Leeward Islands in the same year; the last time this occurred was in 1999, when Category 4 Hurricane Lenny and Category 2 Hurricane Jose hit the islands. Prior to that, the last twin storms to affect the Leeward islands in the same year were Category 4 Hurricane Luis and Category 1 Hurricane Marilyn of 1995. The only previous time on record that two major hurricanes have affected the Leeward Islands was in 1899, when a Category 3 and a Category 4 storm passed through.
|Figure 5. Visible satellite image of Hurricane Jose as of 10:30 am EDT Monday, September 18, 2017. Jose’s strongest thunderstorms are just north of the hurricane’s partially exposed low-level center. Image credit: NASA/MSFC Earth Science Branch.|
A weakening Jose will keep us guessing for days to come
On satellite, Hurricane Jose was looking more like a nor’easter than a tropical cyclone, but it remained a minimal hurricane as of 11 am EDT Monday. Located 265 miles east-southeast of Cape Hatteras, Jose was moving north at 9 mph with top sustained winds of 75 mph. Jose was continuing its long battle with southerly wind shear, which was around 35 knots as of Monday morning. Nearly all of Jose’s intense thunderstorms were located north of its center, with a band of heavy thunderstorms that resembled a cold front extending to the southeast. Jose’s inner structure is increasingly tilted to the north with height, and satellite loops show that Jose is taking on the familiar comma shape of an extratropical storm. By Tuesday, Jose will be moving north over SSTs cooler than the 26°C (79°F) threshold for tropical development. On the other hand, wind shear over Jose will be slackening later this week, and there are no strong fronts or upper-level troughs that would hasten Jose’s conversion to a midlatitude storm. Phase-space diagrams from Florida State University suggest that Jose will remain warm-core (tropical) in nature all week. The official NHC outlook as of 11 am Monday predicts that Jose will become post-tropical by Thursday, though.
Whatever its classification, Jose remains on track to bring gale-force winds and drenching rains to southeast New England, especially with Jose’s asymmetry putting the strongest thunderstorms to the north of its center. Models agree that Jose will continue moving north and then northeast, and NHC predicts its center will be around 200-300 miles south of Cape Cod by Wednesday. A tropical storm warning is in effect for southeast parts of Rhode Island and Massachusetts, with a tropical storm watch for coastal sections of New Jersey, New York, and Connecticut. Rainfall could total 3 - 5” across far southeast Massachusetts (see Fig. 6). Minor to moderate coastal flooding is possible.
|Figure 6. Predicted rainfall from Hurricane Jose. Image credit: NOAA/NWS NHC and WPC.|
Long-term outlook for Jose
Models are in general agreement that Jose will begin to carve out a clockwise loop (the second of its long life) southeast of New England later this week, with Jose possibly heading back toward the west by this weekend. The 0Z Monday GFS and European model ensembles show a wide variety of post-loop tracks for Jose. Almost half of the GFS and Euro ensemble members bring Jose onto the U.S. East Coast on Sunday or Monday, with the other tracks remaining well offshore (see Figures 7 and 8). The UKMET model also has Jose heading west by next Monday, and the 6Z HWRF model carries out a much tighter and faster loop, bringing Jose into New Jersey this Friday.
|Figure 7. The 20 track forecasts for Jose from the 0Z Monday, September 18, 2017 GFS model ensemble forecast. Image credit: CFAN.|
|Figure 8. The 50 track forecasts for Jose from the 0Z Monday, September 18, 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. Image credit: CFAN.|
Jose’s long, lingering track may keep unsettled weather and high surf across southeast New England through the latter part of this week. These impacts should gradually lessen as Jose weakens. The bigger question is how Jose might affect Maria’s track. There are two main possibilities:
—Jose (or its remnants) will produce a weakness in the broad ridge steering Maria toward the west-northwest. In the absence of other major steering currents, Maria will tend to move toward the weakness, thus giving Maria an increasing northward component to its motion by later this week. This is very good news for the U.S. East Coast. Had Jose not been in the picture, the ridge might well have been strong enough to keep Maria plowing west-northwest (and even with Jose, the ridge might still be just strong enough to produce a U.S. landfall, as suggested in the 12Z Monday run of the GFS model).
—If Jose manages to hang on as a post-tropical cyclone into next week, Maria could get close enough to produce Fujiwhara interaction, where two cyclones near each other rotate counter-clockwise around a common point between them. This would also be good news for the East Coast, since the Fujiwhara effect would tend to push Maria northeastward away from the coast.
|Figure 9. Depiction of the Fujiwhara effect as it might play out with Jose and Maria early next week, based on the 0Z Monday, September 18, run of the European model. Model images courtesy tropicaltidbits.com.|
A last burst of strength for Tropical Depression Lee
After losing virtually all of its showers and thunderstorms (convection), Tropical Depression Lee produced a surprise burst of activity early Monday in the eastern tropical Atlantic. Even so, it remained a tropical depression as of 11 am EDT Monday, and Lee's new convection was poorly organized. All signs are that strong wind shear and dry air will finish Lee off as a tropical cyclone by Tuesday morning, with no threat to land.
|Figure 10. Infrared satellite image of Tropical Depression Lee at 11:15 am EDT Monday, September 18, 2017. Image credit: NOAA/NESDIS.|
Bob Henson co-wrote this post.
Jeff Masters does a 30-minute Q-and-A on hurricane modeling and the climate change/hurricane connection in a free Coursera course called, Hurricanes: What’s Next? taught by WU-co-founder and University of Michigan professor Dr. Perry Samson. This Teach-Out, opened for enrollment at noon on Monday, is for anyone interested in wondering about the science of hurricanes, hurricane forecasting and monitoring -- and whether these storms are being driven by climate change.