(Repeats for wider distribution)
By Karen Braun
CHICAGO, Sept 19 (Reuters) - Two major hurricanes, Harvey and Irma, have made landfall in the United States in the past month, and it is possible that Hurricane Maria will strike along the East Coast next week.
Maria is the latest Atlantic hurricane in a very active 2017 season and is already an extremely dangerous storm. Maria crept toward the U.S. Virgin Islands and Puerto Rico on Tuesday after ripping through the small island nation of Dominica, causing widespread devastation.
Maria rapidly intensified in just 24 hours from a Category 1 to a Category 5 hurricane by Monday evening. As of Tuesday morning, Maria retained its Category 5 status, which requires sustained winds in excess of 156 miles per hour (251 km per hour).
After scraping by the Turks and Caicos and southeast Bahamas this weekend, the forecast for Maria is less certain, but a U.S. landfall sometime next week cannot be ruled out. (reut.rs/2xOUM3m)
Whether Maria stays out over the Atlantic or curves back toward the coastal United States most directly depends on the upper-air pattern over the continent and the fate of Hurricane Jose, which still lingers well off the East Coast. (reut.rs/2jGyieX)
Early on in the life cycle, most Atlantic hurricanes move to the west or northwest among the tropical trade winds. But as they drift further north, they eventually get caught up in the mid-latitude westerly winds, which turn the storm track to the north and then northeast or even east.
In the mid-latitudes, eastward-moving troughs of low pressure and ridges of high pressure in the upper atmosphere can strongly influence the motion of Atlantic hurricanes, especially once they reach latitudes parallel with the eastern U.S. coastline.
Upper atmospheric ridges and troughs tend to become stronger into September and beyond as the north-south temperature difference over continental North America widens as summer ends and autumn sets in. This is why the northeast-curving hurricane track is climatologically favored after the Sept. 10 peak of Atlantic hurricane season. (reut.rs/2xL0V0t)
If a strong low-pressure trough is moving off the East Coast of North America at the same time a hurricane is advancing up the coast, the storm will likely be carried off to the north and east at a quick clip, away from the continental United States and out into the open ocean.
But if a strong high-pressure ridge dominates along the East Coast or out over the North Atlantic Ocean, the motion within the ridge forces the hurricane westward along the path of least resistance. A storm or hurricane cannot penetrate a high-pressure system.
In the case of Maria, a massive ridge of high pressure will be parked over eastern North America and the North Atlantic for roughly the next 10 days, but there is a chance the ridge breaks down earlier than expected. If it does, Maria could be pulled away from the coast before it can do too much damage or any at all.
But if the ridge lingers, Maria could meander over toward the Carolinas and potentially move onshore by the middle of next week. Under this scenario, residents along the U.S. East Coast need to root for Hurricane Jose to stay alive in order to protect them from Maria.
If Hurricane Jose can hang on another week or so, even if it gets downgraded to a weak post-tropical storm, it could literally prevent Maria from slamming the U.S. coastline, which is a possibility for early or mid-next week.
The strong ridge of high pressure to Maria’s north would favor a more westward track, but Jose is a weak point within this ridge and could offer Maria an exit path away from the U.S. coast. (reut.rs/2jFFnfD)
As a tropical cyclone, Jose has a distinct center of low pressure. So if it stays wedged in the larger, dominating ridge of high pressure until Maria moves sufficiently close, Jose may pull Maria away from the coast just as a low-pressure system moving off the coast would normally do.
But all of this depends on the timing, which is largely uncertain, given that it is still one week away. If the ridge breaks down first, Maria could get carried away out to sea without Jose. If the ridge deepens or if Jose dissipates, the U.S. coastline – most likely near the Carolinas – could inadvertently welcome Maria ashore.
As of early Tuesday, Hurricane Jose was a Category 1 storm with sustained winds reaching 75 mph (121 km/h), and was expected to remain off the U.S. East Coast without making landfall or causing significant interruptions.
The official forecast from the National Hurricane Center only extends five days, but Jose should linger at least through Saturday with tropical storm status. But East Coast residents may hope Jose can stick around just a couple days longer.
Editing by Jeffrey Benkoe