Hurricane Irma strengthens to Category 4 on its track toward the US

It's looking more likely that Hurricane Irma will affect the US coast - potentially making a direct landfall - starting Frida, local time. The powerful storm strengthened to a Category 4 today with maximum sustained winds of 130m/h (209km/h).

As it tracks west toward the Caribbean, hurricane warnings have been issued for portions of the Leeward Islands and the Greater Antilles. A hurricane warning is in effect for Puerto Rico.

"Preparations within the warning area should be rushed to completion," the National Hurricane Center said in an update on Monday afternoon.

Over the weekend, the forecast track for this potentially devastating hurricane shifted south and west. It seems likely now that the storm will impact or strike the US coast early next week, although meteorologists don't know exactly where. Florida and the Gulf Coast continue to be at risk. The East Coast, including the Carolinas and the Delmarva Peninsula, are also potential candidates for landfall - or, at the very least, heavy rain, strong winds and coastal flooding.

Predictions will improve over the coming days, narrowing down exactly which region will endure the effects of the season's next major hurricane.

Irma has entered into a favorable environment for strengthening, with warm sea surface temperatures and favorable upper-level winds allowing the storm to intensify even more over the next 24 hours. As of 11am Monday (local time), the National Hurricane Center predicted the storm will pass just north of the island of St. John on Wednesday morning (local time) as a Category 4 with winds over 209km/h.

Late Sunday afternoon (local time), Hurricane Hunters began regular flights into Irma, providing extremely valuable data that has improved forecasts. The immediate track of Irma through the middle of the week is not much of a question at this point; an area of high pressure is firmly in place over the central Atlantic, preventing Irma from recurving and escaping out to sea. That high won't move much over the next several days, steering Irma due west into the Leeward Islands by midweek.

This enhanced satellite image made available by the NOAA GOES Project shows Irma, in the middle of the Atlantic Ocean. Photo / AP

Overnight, both the American and European models started to show more consistency in a forecasted track for Irma that increases the chances of impacts on the US coast. Irma will probably continue to be suppressed by the strong Atlantic high pressure beyond Wednesday, keeping the storm at major hurricane status and on a trajectory that places the storm in close proximity to Florida by next weekend.

Chances of a US landfall have increased

Forecasts beyond the five-day mark are still full of uncertainties, but the trend in both the American and European ensemble members is concerning. It's becoming less likely that Irma will escape out to sea, and the chances of a US landfall have increased.

At this point, trying to predict the exact location for Irma's landfall is no better than a guessing game. There is strong agreement in Irma's path through Friday, at which point Irma will probably be a major hurricane located just to the south of the Bahamas. Beyond that, the large-scale features that will ultimately control Irma's final destination are not predictable at this point.

Given what we know at this juncture, it's best to plan for potential impacts rather than exact forecasts. The National Hurricane Center is forecasting tropical storm conditions to begin affecting Florida by late Friday afternoon. All of the usual hazards are at play here; strong winds, heavy rain and dangerous storm surge. Storm surge may become the largest concern over the next few days, given the amount of time that Irma is spending over open water combined with the low-lying topography of southern Florida.

Again, it should be noted that the forecasted track for Irma will continue to change as more aircraft data on the storm is received and as the large-scale environment features become more clear. At this point, residents from the gulf all the way to Maine should take special interest in forecast updates for Irma throughout the week.