“Hurricane” Hal Needham is a storm surge scientist who specializes in data-driven storm surge analysis. He is the founder and president of Marine Weather and Climate.
The National Hurricane Center's most recent update forecasts Hurricane Joaquin to track farther east than previous forecasts. This change reflects eastward shifts in various models, such as HWRF, GFS and UKMET, to reflect solutions closer to the ECMWF (European) model, which all along has been predicting Joaquin to take an eastward turn.
While this updated forecast provides a collective relief for many along the Eastern Seaboard, it's not time to celebrate yet. Hurricane Joaquin is just one player in a complex drama that is taking place along the U.S. East Coast, and, in a sense, other characters in this play will not allow Joaquin to "miss" the East Coast.
A large, strong area of high pressure is building over Eastern Canada, and the gradient between Joaquin and this dome of high pressure will generate strong onshore winds for more than four consecutive days from North Carolina through New England. This situation will play out regardless of Joaquin's exact track. Persistent northeast winds will cause prolonged storm surge flooding and coastal erosion, particularly from Virginia through the New York City area.
The maps below show GFS model output. These maps were initialized (run) at 1200UTC (8 a.m Eastern time) on Thursday, and predict conditions for 1200UTC (8 a.m. Eastern time) on Saturday and Sunday. Note the tightly packed isobars in boxes 1 and 2, which are predicted to occur 24 hours apart.
The two maps below depict ECMWF model forecasts for the same times (1200 UTC/ 0800 EDT on Saturday and Sunday). This model also predicts Joaquin will be centered near the Bahamas on Saturday, but predicts the storm to track northeast, away from the U.S. mainland on Sunday.
However, notice how the isobars, or lines of equal pressure, stay packed in the boxes on both of these maps as well. When we step back and look at the scale of this widespread wind event, we begin to understand why Joaquin won't fully "miss" the U.S. East Coast, even if it tracks out to sea.
Unfortunately, these strong winds will persist four or five days, which spells trouble because the East Coast will need to endure at least 10 high tide cycles during this surge event. Although surge levels may not reach as high as Hurricane Isabel (2003) or Sandy (2012) in this region, this prolonged surge will generate substantial flooding and excessive coastal erosion.
In addition to prolonged coastal winds and storm surge, a stalled out cold front will produce torrential rains in the Carolinas and Virginia, with portions of South Carolina forecast to receive more than 15 inches of rain through late Sunday.
The combination of prolonged onshore winds, storm surge, beach erosion and torrential rains will produce substantial weather impacts along much of the Eastern Seaboard, regardless of Joaquin's exact track.