Hurricane Joaquin: Cautious optimism for the East Coast

Good afternoon.

I think everyone knows by now that Hurricane Joaquin is pounding the Bahamas as an intense storm with destructive wind, rain and storm surge. We have also been closely monitoring the models and the latest information is promising. That said, it is still important to know that some models continue to show a US landfall along the east coast, although that number is decreasing. In addition, the models are fickle and it wouldn’t take a big change in the upper-level pattern to send Joaquin towards land. Hopefully this weekend we can close the book on this and end this anxiety. Rainfall is likely a decreasing threat to the Northeast, but catastrophic rainfall flooding is likely in the Carolinas and Virginia over the next couple days.

Current Situation

Joaquin remains an extremely dangerous hurricane, although the intensity has leveled off or decreased slightly. It remains located in the central Bahamas, very close to Cat Island, moving slowly northward after a slow three-quarter loop over the islands. Maximum sustained winds are likely around 125 mph based on recent aircraft data, suggesting that Joaquin may have weakened to a Category 3 hurricane (which is still extremely dangerous). The minimum central pressure has risen to about 942 mb, after peaking yesterday evening at 931 mb. There are clear signs that Joaquin is undergoing an eyewall replacement cycle, as described yesterday.

Possible Impact Scenarios

It is likely that there will be fluctuations in the intensity of Joaquin over the next 12 to 24 hours as the eyewall replacement cycle continues, but Joaquin should remain at least a Category 3 hurricane over that time. Once completed, a small window of opportunity for re-strengthening should exist on Saturday as Joaquin moves away from the Bahamas and shear remains low. Beyond tomorrow, there is still significant uncertainty in the long-term track, depending on how Joaquin interacts with a vigorous upper-level trough over the southeastern United States as well as a ridge to the northeast which may break down. The possible scenarios all remain in play as below, and the impacts to the Northeast and Mid-Atlantic will also be mentioned for each scenario.

Scenario 1: Southeast direct hit (5% chance)

While most models have long shifted away from this possibility, the CMC model continued to insist as late as 06Z this morning that Joaquin will make landfall in the Southeast, somewhere between Cape Hatteras and Savannah. The 12Z CMC has moved away, joining most of the other models in sparing a US landfall. I would consider this to be a very low probability scenario now as the trough does not look vigorous enough to allow Joaquin to be fully captured and phase into the Carolina coast. Nonetheless, I will continue to mention the possibility here that somehow Joaquin weakens enough to be captured to be trough to the west. Regardless, extremely heavy rain is ongoing in the Southeast and will continue to fall, with widespread amounts of 10 to 16 inches likely across South Carolina and southern North Carolina. Upstate South Carolina may see as much as 30 inches in a few locations. Severe, possibly catastrophic, flooding is likely.

12Z GFS rainfall forecast today for the Southeast. Notice the extreme rainfall. This is not directly related to Joaquin.

12Z GFS rainfall forecast today for the Southeast. Notice the extreme rainfall. This is not directly related to Joaquin.

Scenario 2: Mid-Atlantic direct hit (5% chance)

Likewise, this scenario has lost practically all model support. Similar to Scenario 1, it appears the trough will not be able to swing Joaquin into a Fujiwhara interaction far enough south to impact the Mid-Atlantic directly. A few GFDL and CMC runs have shown this scenario recently but they have all backed off, as have most ensembles. For the Mid-Atlantic, direct impact is unlikely. Nonetheless, heavy rainfall is also expected for those areas, along with storm surge flooding unrelated to Joaquin in some coastal areas from New Jersey to North Carolina. I wouldn’t close the book on this possibility, but it is highly unlikely.

Scenario 3: Northeast direct hit (15% chance)

While most models are out to sea, there are still many – including the HWRF, GFDL, CMC and some GFS runs – that are dangerously close to southern New England. It is possible that Joaquin may try to turn northwest or north-northwest at higher latitudes should the trough (by then likely a closed low) interact with Joaquin this weekend. Alternatively, Joaquin could try to go out to sea later and the blocking ridge to the north remains stronger than expected. That might be enough to swing Joaquin towards landfall in the Northeast by Monday or Tuesday, most likely east of New York City. I would consider the potential for a direct hit greater in southeastern Massachusetts (Cape Cod, Nantucket and Martha’s Vineyard) and eastern Maine with a lower chance still existing for other areas in the Northeast.

If this scenario verifies, significant coastal flooding and wind damage is still possible, especially in exposed areas where hurricane force winds (at least in gusts) may be possible. Since it is likely that Joaquin would be transitioning to a post-tropical cyclone, rainfall would likely be focused west of the center, with the strongest wind and surge well to the east despite relatively little rainfall. Many land areas would receive tropical storm force winds with stronger gusts. Power outages would be widespread with significant tree damage. This would be similar to Hurricane Edna in 1954 and the 1869 Saxby Gale.

12Z CMC ensemble run today, showing a few members showing landfall in southern New England on Tuesday. This isn't very likely but cannot be ruled out.

12Z CMC ensemble run today, showing a few members showing landfall in southern New England on Tuesday. This isn’t very likely but cannot be ruled out.

Scenario 4: Northeast indirect hit (25% chance)

In this scenario, Joaquin remains over water just south/east of southern New England as it escapes out to sea, possibly after a slight tug westward in the middle latitudes. However, it would be close enough to produce land impacts with strong winds, heavy rainfall and minor coastal flooding, along with very high waves offshore. The closest approach would likely be late Monday into Tuesday. This is supported by the GFDL and CMC models and some GFS runs.

The areas that would see the greatest impacts would be southeastern Massachusetts, especially Cape Cod, Nantucket and Martha’s Vineyard. Tropical storm force winds would be likely in those areas, along with very high waves. Some flooding would be possible, both coastal and inland, along with isolated to scattered power outages. Windy and rainy conditions would also be possible for other parts of coastal southern New England, particularly Rhode Island and eastern Massachusetts. This would be similar to Hurricane Earl in 2010 and Hurricane Arthur in 2014.

12Z GFDL run from today. Hurricane Joaquin - likely a Category 1 at this point - is located southeast of Nantucket, with rain and wind reaching inland.

12Z GFDL run from today. Hurricane Joaquin – likely a Category 1 at this point – is located southeast of Nantucket, with rain and wind reaching inland.

Scenario 5 – Out to sea far from the Northeast coast (50% chance)

This is now the most likely scenario and the possibility has increased. The GFS has caved to the ECMWF, which had suggested this the entire week even when all other models insisted on landfall. The HWRF and NAVGEM models also support this scenario now. In this case, the only impacts for the Northeast will be high surf and rip currents at the beaches, along with breezy conditions due to the gradient with the ridge to the north. Significant land impacts are possible in Bermuda and Atlantic Canada, however.

12Z GFS run from today for early Tuesday. It had long insisted on landfall but now has Joaquin safely out at sea.

12Z GFS run from today for early Tuesday. It had long insisted on landfall but now has Joaquin safely out at sea.

12Z ECMWF run from today. Continues to show Joaquin well out to sea, after a close call with Bermuda. This model has consistently shown this solution.

12Z ECMWF run from today. Continues to show Joaquin well out to sea, after a close call with Bermuda. This model has consistently shown this solution.

Conclusion

Things are definitely looking much more promising than they were 24 or especially 48 hours ago. With more and more models sending Joaquin safely out to sea, we may have dodged a huge bullet as it is an extremely dangerous hurricane. However, it is too soon to be precise and this hurricane has surprised us several times. We shouldn’t let our guards down yet, especially in the Northeast. It is a complicated atmosphere with multiple features and slight changes could require adjustments in the probabilities. Make sure you continue to monitor forecasts so that you don’t get surprised at all.

Rainfall unrelated to Joaquin should primarily be a problem from the Mid-Atlantic southward, and especially in the Carolinas. That is because it appears the frontal boundary is reaching farther south than expected. South of DC, rainfall amounts increase dramatically, with South Carolina likely facing the worst of the flooding.

WPC rainfall forecast through Wednesday. While extreme rainfall is likely in the Southeast, most of the Northeast should be spared the heavy rain.

WPC rainfall forecast through Wednesday. While extreme rainfall is likely in the Southeast, most of the Northeast should be spared the heavy rain.

Finally, some models want to develop the upper-level low responsible for the steering of Joaquin. In my opinion, there is a slight chance that low could take on (sub)tropical characteristics and become Tropical Depression Twelve or Tropical Storm Kate. The low has not yet been mentioned by the NHC, but is important to also monitor. We must continue to be vigilant, but things are looking much better for the Northeast and Mid-Atlantic. Have a good and safe weekend!

Forecaster Craig Ceecee

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