TROPICAL STORM BONNIE

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Quote: SPECIAL TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
740 PM EDT WED MAY 25 2016

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

Cloudiness and showers over the western Atlantic Ocean a few hundred
miles northeast of the Bahamas are associated with a newly formed
area of low pressure. Environmental conditions are expected to
gradually become more conducive for development, and a tropical or
subtropical cyclone could form on Friday or Saturday. The low is
forecast to move slowly west-northwestward or northwestward and
approach the southeastern United States over the weekend. The next
Special Tropical Weather Outlook on this disturbance will be issued
by 9 AM EDT on Thursday. For additional information on this system,
see High Seas Forecasts issued by the National Weather Service.
* Formation chance through 48 hours...low...30 percent
* Formation chance through 5 days...medium...60 percent

[Her-icane]

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JM

Quote: Odds of a Weekend Tropical Depression Rise; Dodge City Dodges Multiple Tornadoes


By:Jeff Masters and Bob Henson , 3:36 PM GMT on May 25, 2016


Showers and thunderstorms continue over portions of the Bahamas and nearby waters in association with an upper-level trough interacting with a weakening cold front. On Wednesday morning, NHC designated this area of interest as Invest 91L. This activity is expected to coalesce into an area of low pressure on Friday a few hundred miles north of the Bahama Islands. This low has the potential to develop into a tropical depression as it moves northwest towards the Southeast U.S. coast over the weekend. Sea surface temperatures (SSTs) over the Bahamas are about 28 - 29°C (82 - 84°F), which is 1 - 2°C (1.8 - 3.6°F) above average. These waters are plenty warm enough to support formation of a tropical storm. Phase space diagrams from Florida State University have been consistently showing over the past few days that this storm will be a symmetric warm core system--technical lingo for a storm that is tropical in nature, rather than subtropical or extratropical.



Figure 1. The area of disturbed weather near the Bahamas that we're tracking, as seen by MODIS on Tuesday afternoon, May 24, 2016.



Figure 2. Predicted wind speeds for the Southeast U.S. at 2 pm EDT (18Z) Monday, May 30, 2016 from the 00Z Wednesday, May 25 run of the European model (left) and the 06Z Wednesday May 25, 2016 run of the GFS model (right). Both 5-day forecasts were predicting a possible tropical depression off the Georgia/South Carolina coast. Image constructed using our wundermap with the "Model Data" layer turned on.

Increasing model agreement on genesis
In my 2013 blog post, Genesis of New Atlantic Tropical Cyclones: Which Model Should You Trust?, I explained that we have three models that have proven to be fairly reliable for predicting the genesis of tropical depressions up to four days in advance: the American GFS model, the European ECMWF model, and the British UKMET model. About 50% of the time, at least one of these models will successfully predict tropical cyclone genesis up to four days in advance. When all three models agree on genesis, confidence increases in the forecast. On Tuesday, the UKMET model was not forecasting genesis, while the GFS and European models were. However, the Wednesday morning (00Z) runs of all three of these models showed the potential for Invest 91L to develop into a tropical depression a few hundred miles north of the Bahamas this weekend; this increases our confidence that genesis will occur. In a special Tropical Weather Outlook issued at 8:15 am EDT Wednesday, the National Hurricane Center bumped up their development odds in the 2-day and 5-day time ranges to 10% and 50%, respectively.

Invest 91L likely will not have enough time over water to become a strong tropical storm or hurricane, so heavy rain is the main concern from this system. The 00Z Wednesday runs of the models indicated a possible threat to the coasts of northern Florida, Georgia, or South Carolina early next week--though the European model showed the storm staying just off the coast through next Wednesday. I'll keep you updated each day this week with the latest prognosis for this potential early-season storm. Should it become a tropical storm, it would be named Bonnie.

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AL, 91, 2016052600, ,BEST,0,266N,677W,25,1015,LO,34,NEQ,0,0,0,0,1017,140,100,0,0,L,0, ,0,0,INVEST

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8AM

Quote: SPECIAL TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
825 AM EDT THU MAY 26 2016

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

1. A low pressure area centered between Bermuda and the Bahamas is
gradually becoming better defined while shower activity is
increasing. Environmental conditions are expected to become more
conducive for tropical or subtropical cyclone formation on Friday
while the system moves west-northwestward or northwestward toward
the southeastern United States coast. With the Memorial Day weekend
approaching, all interests along the southeast coast from Georgia
through North Carolina should monitor the progress of this low. An
Air Force reconnaissance plane will be scheduled to investigate
this low on Friday. The next Special Tropical Weather Outlook on
this disturbance will be issued by 3 PM EDT today. For additional
information on this system, see High Seas Forecasts issued by the
National Weather Service.
* Formation chance through 48 hours...medium...50 percent
* Formation chance through 5 days...high...70 percent

[Batt2fd]

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8AM

Quote: SPECIAL TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
745 AM EDT FRI MAY 27 2016

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

Shower activity associated with the low pressure area located
between Bermuda and the Bahamas continues to show signs of
organization, and the circulation of the low has become a little
better defined overnight. Environmental conditions are generally
conducive for a tropical or subtropical cyclone to form later today
or Saturday while this system moves west-northwestward to
northwestward toward the southeastern United States coast. All
interests along the southeast coast from Georgia through North
Carolina should monitor the progress of this low. An Air Force
Reserve Hurricane Hunter aircraft is scheduled to investigate the
low this afternoon. The next Special Tropical Weather Outlook on
this disturbance will be issued by 3 PM EDT this afternoon. For
additional information on this system, see High Seas Forecasts
issued by the National Weather Service.
* Formation chance through 48 hours...high...90 percent
* Formation chance through 5 days...high...90 percent

[SevereWxEnthusiast]

We've got a floater on it, Here is the link for a flash based animation of the visible sat feed:

91L visible flash loop

[Her-icane]

JM

Quote: Tropical/Subtropical Depression Could Form Today in Northwest Atlantic
By: Jeff Masters and Bob Henson , 3:50 PM GMT on May 27, 2016


Formation of a tropical or subtropical depression appears imminent on Friday or Saturday in the waters between the Bahamas and Bermuda as Invest 91L moves west-northwest or northwest towards the Southeast U.S. coast. Should it become a named storm, it would be called Bonnie.

Satellite loops show that 91L has a pronounced spin near the surface that has improved in organization since Thursday--the circulation is less elongated, and more circular. However, there was only a modest amount of heavy thunderstorm activity that was not changing much in areal coverage associated with 91L on Friday morning. The latest pass from the ASCAT satellite showed an area of surface winds near 35 mph in the heaviest thunderstorms to the north of the center. Sea surface temperatures (SSTs) near 91L's center were about 26°C (79°F), which is 1 - 2°C (1.8 - 3.6°F) above average. These waters are only marginally warm enough to support formation of a tropical storm, and 91L has taken on some characteristics of subtropical system instead of a tropical system. As I explain in my Subtropical Storm Tutorial, a subtropical storm typically has a large, cloud free center of circulation, with very heavy thunderstorm activity in a band removed at least 100 miles from the center. The difference between a subtropical storm and a tropical storm is not that important as far as the winds they can generate, but tropical storms generate more rain.

Wind shear on Friday morning had fallen to the moderate range, 10 - 20 knots, increasing the odds of development. A large area of dry continental air lies to the west of 91L, and this dry air is interfering with development. A hurricane hunter aircraft is scheduled to investigate 91L on Friday afternoon.


Figure 1. Latest satellite image of 91L.



Figure 2. Predicted wind speeds for the Southeast U.S. at 2 am EDT (06Z) Sunday, May 29, 2016 from the 00Z Friday, May 27 runs of the European model (left) and GFS model (right). Both models had the storm just off the coast of South Carolina. Image constructed using our wundermap with the "Model Data" layer turned on.

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Hunter is up!

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3pm

Quote: SPECIAL TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
300 PM EDT FRI MAY 27 2016

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

Shower and thunderstorm activity has become more concentrated with
the area of low pressure located about 450 miles southeast of
Charleston, South Carolina. An Air Force Reserve Hurricane
Hunter aircraft is currently investigating the low to determine if
it has acquired a well-defined surface circulation. Environmental
conditions are favorable for this system to become a tropical
cyclone later today or on Saturday while it moves west-northwestward
toward the southeastern United States coast. Interests from Georgia
through North Carolina should monitor the progress of this low.

If advisories are not initiated this afternoon, the next Special
Tropical Weather Outlook on this disturbance will be issued by
8 PM EDT this evening. For additional information on this system,
please see High Seas Forecasts as well as products issued by your
local National Weather Service forecast office.
* Formation chance through 48 hours...high...90 percent
* Formation chance through 5 days...high...90 percent

&&
High Seas Forecasts issued by the National Weather Service can be
found under AWIPS Header NFDHSFAT1 and WMO Header FZNT01 KWBC.

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Special Message from NHC Issued 27 May 2016 20:07 UTC
NHC will
initiate advisories on Tropical Depression Two at 5 pm EDT/2100 UTC.
This will include a TS Warning for the South Carolina coast.