Emily, A Potential Threat?


TDEmilyTUB6am20170801-0900UTC
The Bermuda Weather Service Tropical Update Bulletin for this morning’s 6am update: Closest point of approach to Bermuda within 72 hrs (3 days) is forecast to be 236 nm to the NNW, 3 pm Thu, Aug 3, 2017. However, this system may move closer to Bermuda after this time period.

Yesterday morning, Tropical Storm Emily quickly formed in the Gulf of Mexico, just west of Tampa, Florida. The tropical storm made landfall south of Tampa a few hours later with maximum sustained winds near 40 kts. Through Monday evening and overnight, Emily tracked across the Florida peninsula, weakening to a tropical depression and emerged into the southwestern Atlantic early this morning. Tropical Depression Emily is a “Potential Threat” to Bermuda.

What does a “Potential Threat” mean?

PotentialThreatGlossary

This means that the center of a tropical cyclone (e.g. TD Emily) is expected to pass within 400 nautical miles of Bermuda in the next 72 hours. As of the 6am local time update from the National Hurricane Center and Bermuda Weather Service, Emily is expected to pass under 250 nautical miles away from the island on Thursday. It is important to note that these threat designations do not suggest that the tropical cyclone in question will result in adverse weather as it passes.

[See the BWS Glossary]

Another Emily?

Yes. The National Hurricane Center has six lists of names, and a new list is started for each hurricane season. The lists are then used in rotation, so every six years the same list of names is used again. A name is retired from the list is a storm is ‘so deadly or costly that the future use of its name on a different storm would be inappropriate for reasons of sensitivity’.  During the annual meeting by the World Meteorological Organization committee, representatives can suggest the retirement of a name and vote on the replacement name.

‘Emily’ has been a name on the Atlantic name lists since ‘Eloise’ was retired after the 1975 Hurricane Season. There have now been 7 tropical storms or hurricanes with the name ‘Emily’.

[More on Hurricane Names from the NHC]

What can Bermuda expect from Emily 2017?

Short answer: not much. As Emily passes on Thursday, the Bermuda Weather Service expects moderate winds (10-15 kts), slight seas (1-2 feet, inside the reef), and only isolated or scattered showers with a risk for thunder to dampen Emancipation Day, the first day of Cup Match.

EastUS_Annotated
GOES-13 infrared imagery at 1045 UTC (7:45am local time) showing tropical depression Emily (red circle), a stationary front (red and blue line), and Bermuda (cyan circle).

Emily is not expected to change much in strength, possibly re-strengthening to a weak tropical storm at most. Strong vertical wind shear over Emily is allowing deep layered dry air to be entrained from the west. This is limiting the depression’s ability to maintain convection, organize, and strengthen despite being over the very warm waters of the Gulf Stream.

Showers and thunderstorms ahead of the stationary front to the west have already been the theme for Bermuda. Wind gusts reached gale force in and around some of those showers (official peak gust reached 35 kts at the airport yesterday, about the same as wind gusts currently around Emily). While showers and thunderstorms are expected to continue through Friday, high pressure building in from the east may allow dry (and even sunny) spells in between showers.

As Emily interacts with the front over the next 36-48 hours, it is expected to transition to a post-tropical cyclone. Emily is forecast to track northeastwards, along the stationary front over the next five days. The flow ahead of Emily is expected to gradually lift the stationary front away from Bermuda starting late today through her closest approach on Thursday. This allows high pressure to build in from the east, slowly reducing the coverage of shower activity and allowing winds to slacken. Emily then passes Bermuda and the flow behind her swings the front back towards Bermuda, bringing increased chances for showers on Friday morning.

Follow the Bermuda Weather Service and National Hurricane Center for any changes to their forecast.

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