Hermine a major coastal threat, inland threat highly uncertain

Good evening.

First, I apologize for the lack of posts this week. I have been incredibly busy with school and wrote a tropical report for class, plus I have been practicing on-air broadcasts. Nonetheless, the models jumped to a more dangerous solution with Hermine in the last couple days. The storm already did significant damage in northern Florida and southern Georgia from wind and storm surge.

This weekend, the Northeast and Mid-Atlantic coast faces a potentially ominous threat from Hermine as a ridge of high pressure is expected to wrap around it, blocking any movement. The greatest impacts will be felt at the beaches with high winds, erosion, storm surges and high waves as a result of the onshore flow. Most models do not bring Hermine ashore, but it still needs to be watched. The threat will last through the entire Labor Day weekend and well into next week.

Key points

There are several important points that must be made:

1) Hermine may lose tropical characteristics while off the east coast, transitioning into a subtropical or extratropical low pressure area (think Nor’easter). Using lessons learned during Sandy, the structure of the storm shouldn’t be our concern. For the purposes of this post, I will continue to call it a tropical storm or hurricane. The impacts won’t change regardless of the structure.

2) Consider cancelling plans to travel to any east coast beach from the Delmarva northward to New England. This will be a long duration event so you won’t have an opportunity at any time this weekend (or next week).

3) While comparisons to Sandy are inevitable, this is a completely separate situation. The trough coming down – if there is one – is much weaker. The main driving force in the synoptic setup is a strong ridge over eastern Canada, with ridges also building to the east over the north Atlantic and the west over the Ohio Valley. Also, Hermine is (and will continue to be) much smaller than Sandy, with tropical storm winds extending out to only about 1/6 the area.

Current situation
Color-enhanced satellite image of Tropical Storm Hermine as of 5:45 pm EDT September 2, 2016.

Color-enhanced satellite image of Tropical Storm Hermine as of 5:45 pm EDT September 2, 2016. (NHC/NOAA)

Hermine remains a fairly well organized tropical storm. Currently located near Charleston, SC, it should track offshore shortly, with most of the rain located inland over the Piedmont. Sustained winds have decreased to about 50 mph based on beach reports although it is possible stronger winds exist offshore. The minimum pressure remains quite low at about 991mb. For comparison, Hermine had winds of about 85 mph when it made landfall in Florida, and the central pressure at the time was about 984mb.

Sea surface temperature map for the Mid-Atlantic coast on September 1, 2016. (NOAA)

Sea surface temperature map for the Mid-Atlantic coast on September 1, 2016. (NOAA)

Once Hermine returns over water, strengthening is possible, particularly late tomorrow through Sunday as it reaches the Gulf Stream. SST’s are as high as 29°C (84°F) as far north as off the Delmarva. The oceans are somewhat cooler closer to the coast, but certainly not cool. That will allow the storm to at least maintain its strength and likely intensify. Baroclinic forcing due to a nearby frontal boundary will also enhance Hermine. Hence it is likely that Hermine will regain hurricane intensity (as a tropical, subtropical or post-tropical entity) and perhaps approach Category 2 intensity in the most aggressive models. Those are higher than the NHC forecasts. There are four possible scenarios that I see in terms of what could happen with Hermine.

Scenario 1: Stalling out well offshore (20% chance)
00Z GFS September 2, 2016 model run for Monday night. Notice Hermine is well offshore and the rain shield remaining mostly offshore. Unfortunately, most models don't suggest this anymore.

00Z GFS September 2, 2016 model run for Monday night. Notice Hermine is well offshore and the rain shield remaining mostly offshore. Unfortunately, most models don’t suggest this anymore.

This is the scenario advertised by earlier models, but they are backing off on it. Of the four scenarios, this is the least severe for land areas, but it is still significant. Hermine likely restrengthens into a hurricane, essentially stalling out near 38°N 72°W due to strengthening ridges in all directions.

Strong winds would likely be limited to the beaches, perhaps gusts to 40-50 mph, but much stronger offshore. Inland winds and rain would likely be minimal due to the distance from the storm. Coastal erosion would still be significant due to wave action through multiple tidal cycles.

Scenario 2: Looping closer to shore (50% chance)
18Z GFS September 2, 2016 model run for Sunday night. Tropical storm force winds stretch from near Hampton Roads to Long Island. Breezy conditions extend inland.

18Z GFS September 2, 2016 model run for Sunday night. Tropical storm force winds stretch from near Hampton Roads to Long Island. Breezy conditions extend inland.

Most models appear to favor this scenario, including recent GFS runs and the ECMWF. It is a much more severe scenario for the coastal areas, particularly from the Delmarva to Long Island. The ridge continues to pump up to the north and west, but farther away or not as strong. At the time, what would likely be Hurricane Hermine would be pushed leftward close to the mid-Atlantic coast. The loop would remain about 50 to 150 miles offshore of the Jersey Shore.

Severe winds are likely at the beaches in this scenario, perhaps 50 to 70 mph in exposed areas. Friction inland will reduce the wind there greatly, but gusts to tropical storm force are still possible up to near I-95. Heavy rain is also likely close to the coast. However, the greatest impacts should be storm surge, very high waves and severe beach erosion. Unfortunately, the beach impacts will be enhanced by damage from Hurricane Sandy in 2012 – a lot of it has not been mitigated. The January blizzard also did damage to the lower Jersey shore as well.

Scenario 3: Looping at the beaches (20% chance)
12Z ECMWF September 2, 2016 model run for Monday morning. The center of what would be either Tropical Storm or Hurricane Hermine is located very close to Ocean City, MD.

12Z ECMWF September 2, 2016 model run for Monday morning. The center of what would be either Tropical Storm or Hurricane Hermine is located very close to Ocean City, MD.

Models have slowly trended this way and the 12Z ECMWF actually comes very close to a second landfall along the Delmarva or Jersey Shore. A somewhat weaker ridge to the west, along with a stronger ridge to the east, would allow Hermine to get a “nudge” farther west and either dangerously close to the coast or onshore in the coastal plains, most likely either on Monday or Tuesday. Since the steering currents should remain weak, Hermine would then return offshore and meander close to the coast.

Depending on the intensity and timing, tropical storm force sustained winds are probable with this scenario east of I-95. Hurricane force winds cannot be ruled out in a small area near the beach, at least in gusts. Heavy rain is also likely for a larger area, including along a good part of the I-95 corridor. Once again, coastal flooding is the greatest threat – particularly wave action and storm surges. The exact locations cannot be pinpointed but the entire coast from near Hampton Roads to Cape Cod could experience severe flooding and erosion.

Scenario 4: Inland track (10% chance)
18Z GFS September 2, 2016 model run for Tuesday afternoon showing the 500mb heights. Notice the ridge moving both west and east with a trough trying to push down (it fails in this run). Such *might* allow an alleyway to open northward.

18Z GFS September 2, 2016 model run for Tuesday afternoon showing the 500mb heights. Notice the ridge moving both west and east with a trough trying to push down (it fails in this run). Such *might* allow an alleyway to open northward.

Although no reliable model suggests this possibility at this time, a slight possibility DOES exist in my opinion that Hermine may find an opening to track inland. The 18Z GFS shows a slight weakness in the ridge to the northwest. Such would most likely be between Monday and Wednesday, when the storm would be able to accelerate northwest or north-northwest. Landfall would likely be somewhere along the Jersey Shore or near New York City and Hermine would track northward inland over upstate New York or Pennsylvania (not unlike the 1903 hurricane).

This is highly speculative, given the very low potential at this time, but a dangerous storm surge would be certain near and east of the landfall point (especially if it is a strong storm). Damaging winds and heavy rain would spread well inland. However, specifics cannot be made due to the wide variety of possibilities and timing.

Conclusion

For those near the coast, now is the time to prepare your beach house or boat if possible. This could very well be a significant storm for the Northeast and Mid-Atlantic coast. Although every storm is different, some similarities have been made with the 1962 Ash Wednesday storm and the 1991 Perfect Storm. Inland, the impacts should be much more limited unless an unlikely track is taken as the ridge should protect those areas. Listen to emergency officials in your state, county or community for advice and local meteorologists for local updates.

For those expected to be affected severely, stay safe! Otherwise have a great Labor Day weekend!

Forecaster Craig Ceecee – @Ceecee_Wx

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