Hurricane Irma a Major Threat to the Southeast US, Cool Weather for the Northeast

Happy Wednesday! Some unsettled weather continues for the Northeast today. Then improving weather is likely for the rest of the week. But it will feel more likely early Autumn. Hurricane Irma will become a major threat to the Southeast US this weekend and early next week. More detailed analysis on Irma’s potential future is below.

First for today, a few weak waves of low pressure running will be running along a slow-moving cold front. This will result in multiple rounds of showers and/or t-storms will continue moving through parts of the Northeast, especially near I-95 corridor and coastal plain through much of tonight. Instability is marginal at best. So no severe weather hazards are anticipated. However, some locally heavy rainfall and flash flooding is possible with high precipitable water values over 1.50″.

More improving weather is expected on Thursday, as the cold front moves further offshore. Then Canadian high pressure builds into the Northeast and Mid-Atlantic on Friday and the weekend. But despite more sunshine, temperatures will remain cooler than normal. High temperatures for many areas, will only be in the upper 60s to lower 70s. Some isolated showers are also possible, as shortwave trough and a cold-pool with instability aloft moves Friday and Saturday, mainly over the Interior parts of the Northeast.

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GFS model with temperatures several degrees cooler than normal over the Northeast on Saturday

Meanwhile, Hurricane Irma is now currently moving over Northern Leeward Islands. It is too early to know what impacts the storm has had on the islands. But Irma remains a Category 5 hurricane Irma, capable of catastrophic damage from high winds and storm surge. Irma continues moving west-northwest will continue moving just north of Puerto Rico later today and tonight, then north of Hispaniola on Thursday. While Irma’s strongest winds may avoid these islands, some hurricane force winds are still likely, especially along northern coasts.

On Friday and Saturday, the storm will continue to be steered west-northwestward by a ridge over Western Atlantic move somewhere between Cuba, Bahamas and Turks and Caicos Islands. Irma is expected remain a very powerful hurricane, likely a Category 4 or 5 for much of the time, as it moves over very warm waters. But some fluctuations in Irma’s intensity are likely. Irma may weaken during eyewall replacement cycles that difficult to predict. It also possible the storm’s inflow may be disrupted by the mountains of Hispaniola or Cuba. Irma may will also be running into stronger southwesterly shear from mid-level trough linger over Southeast US.

Then some uncertainty increases, as the full-latitude upper-level trough begins lifting out of Eastern US. Irma is expected to turn more towards the north to northwest, into a weakness in the West-Atlantic ridge, left behind by this trough. Where precisely that turn happen is where the model and ensemble guidance largely diverges. However, there is has been a trend in track forecast further east, with guidance overnight and this morning.

GEFS trending with deeper trough over this Northeast US

GEFS trending with deeper trough over this Northeast US. More weakness in the ridge to for Irma turn more northward, after moving through Bahamas/Cuba

Some shortwave energy digging on downside of West-Coast ridge, may cause the trough to remain somewhat deeper into Northeast this weekend. Thus Irma could turn north-northwestward before reaching Florida and Irma to make landfall over Georgia or the Carolinas. But depending on the track, the storm can still cause some high winds, heavy rainfall and storm surge all along the Southeast Coast. So anyone with interests in these areas should still prepare for major direct impacts from Irma, if not from a landfalling major hurricane.

Later next week, the remnants of Irma may move northward into the Northeast or Mid-Atlantic regions or parts of Eastern AG belt, as interacts with another incoming trough over Northern Plains or Great Lakes. Otherwise, given the current model forecast timing of systems moving across the Northern US Tier, and lack of high latitude blocking over the Atlantic, there remains little risk for Irma to make landfall as a tropical cyclone further north along the East Coast.

Stay tuned for more premium article or video updates on forecast this week and latest Hurricane Irma. Also check the tropical weather dashboard, for the latest on two new tropical storms. Tropical Storm Jose which may threaten the Northern Leeward Islands next week. As well as, Tropical Storm Katia in the Southwest Gulf of Mexico, which will only likely be a threat to Mexico. It’s the peak of the Atlantic hurricane season. So multiple tropical system occurring, aren’t unusual for this time of year.