FLHurricane.com: Vigorous Andrea Upping the Ante

6 June 2013 5:00 AM EDT Update

Tropical Storm Andrea has defied forecasts calling for little or no strengthening, and has become a potent 60 MPH Tropical Storm, and this could be conservative. Additionally, while not forecast, some additional strengthening is actually still possible before landfall.

Andrea has managed to run into a zone of upper-level winds that are actually resulting in two events supportive of intensification:

First, strong upper-level winds that would normally be creating detrimental shear are running in about the same direction Andrea has been traveling overnight, also important that her forward speed has increased, both resulting in net effective shear that is actually quite a bit lower than would be the case if the cyclone was heading to a more right angle of the mean upper-level flow.

Second, these same upper-level winds have created a nice source of exhaust for Andrea's thunderstorms, thereby creating a perpetual entrainment machine: inflow in, inflow out (vacuum) more inflow in, more inflow out (rinse and repeat).

Andrea now exhibits the hallmark of a tropical cyclone that does not necessarily need to reach hurricane status to result in more than just some heavy tropical squalls, and those in its path may wish to consider revisiting their hurricane preparedness plans, as regardless of whether Andrea intensifies further, very heavy rain - with increased risks of inland flooding - some storm surge flooding along the coast, potentially damaging winds - especially in gusts - and isolated tornadoes, are now all possible anywhere from south Florida right up into the Big Bend.

Later in the week, Andrea is forecast to continue at storm intensity as she rides up the east coast. This has necessitated Tropical Storm Warnings to be extended all the way to Virginia.

Ciel

5 June 2013 6:30 PM EDT Update
Tropical Storm Warnings are up for the West Coast of Florida from Boca Grande (Coast between Ft. Myers and Port Charlotte) and the Ochlockonee River (Just south of Tallahassee). Tropical Watches are up from Flagler Beach on the East coast of Florida north to Surf City, NC.

Storm surge flooding of 2-4 ft above ground level, or inundation, expected with TS Andrea from Tampa Bay Northward to Apalachicola

From NWS Melbourne:

5 June 2013 5:30 PM EDT Update
Andrea Forms.

From a special Tropical Weather Outlook:

AN AIR FORCE RECONNAISSANCE AIRCRAFT WAS ABLE TO IDENTIFY A
WELL-DEFINED CIRCULATION IN THE LOW PRESSURE AREA OVER THE EAST-
CENTRAL GULF OF MEXICO LATE THIS AFTERNOON. BASED ON THIS
FINDING...THE NATIONAL HURRICANE CENTER WILL INITIATE ADVISORIES ON
TROPICAL STORM ANDREA WITHIN THE NEXT HOUR OR SO. THIS SYSTEM HAS A
HIGH CHANCE...NEAR 100 PERCENT...OF BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS.

Tropical Storm Watches/Warnings for the West coast of Florida will likely be up soon.

5 June 2013 8:00 AM EDT Update
Development chances are 50/50 now, but even with the flareup overnight, the circulation is still not defined very well. Nonetheless, development may occur within the next 48 hours before its forecast move inland across the Big Bend or Eastern Panhandle tomorrow night.

5 June 2013 5:00 AM EDT Update
Flhurricane.com for complete story & discussion.

As of early this morning, here are the bullet points:
91L's structure is a blend of subtropical and marginally tropical
91L's weather continues to be most pronounced on its eastern half
Conditions for development have turned from unfavorable to marginally favorable
Conditions for development are forecast to become even better over the next day or two

The broad low pressure area being tracked as Invest 91L has been struggling to organize over the past several days, but conditions are now staring to become marginally favorable for subtropical or tropical development.

As of early Wednesday morning, 91L still consists of a broad surface circulation with multiple, competing swirls about an axis of lower pressure, but this could be starting to change.

Late last night convection started flaring up a little closer to the center, and not so far removed as to be completely auxiliary. Concurrent with this event, pressures have been falling, and wind speeds rising. More recently, night vision IR imagery suggests that a center reformation may be trying to take place closer to the deepest convection. Any one of these by itself may not mean much, but taken together, this is characteristic of a sloppy system getting better organized.

The driving forces that have been holding 91L in check are starting to relax, with both shear and dry air decreasing. With upper level winds now aligning themselves a little with the lower levels, 91L is starting to take on a somewhat classic subtropical cyclone look.

At the surface, observations show winds now up to around 35 MPH sustained, with higher gusts. Most of the strongest winds are occurring well removed from 91Ls estimated center, which is also consistent with subtropical cyclones. In fact, a ship report from roughly 350 miles to its east recently reported winds of up to 49 MPH in a thunderstorm.

Recon is tentatively scheduled to fly through Invest 91L later today.

Ciel

4 June 2013 Update

The area in the Gulf, 91L, continues to hang in the gulf, but is starting to show more subtropical characteristics, which ultimately means more rain and breezy conditions over a larger area.

The west side of the system is still involved in a lot of dry air, as the general center itself is still off the tip of the Yucatan. The rainfall is starting to appear in southwest Florida, and will slowly spread northward, most of the rain will likely wind up being in south Florida.

Development wise, it has about a 30% shot to develop in the next 48 hours currently, and as mentioned earlier probably has a better chance to develop into a subtropical system, if at all, than a purely tropical one. Still either could occur, and it just means flooding conditions for parts of Florida as it drifts very slowly through the gulf, more northerly at first before flowing a bit east, which will give more central and north Florida a chance for rain later.

For central Florida late Wednesday night and most of Thursday is the highest chance for rainfall, some rain may linger in south Florida after the system moves over a bit longer, so South Florida still will by far see the most rainfall.

Based on the path of the storm, conditions will possibly be good for a small tornado threat Thursday night in parts of Florida.

Long term florida radar recording SWFWMD Full Florida Radar Recording for 91L Alternate Style

Original Update

Tropical Development is possible this week, and it may impact Florida. At the very least rainfall will be great most of the week, through Thursday when the most likely landfall time would occur on the West Central Florida coastline. As the area currently is very broad, the most likely place to watch for development is the general center near the northeastern tip of the Yucatan Peninsula.

Tropical development chances are only at 20% right now, but conditions are good enough that a possible tropical depression or lower end Tropical Storm may form mid week. Rainfall in central and south Florida will be greatly enhanced by this broad low pressure area this week, as of 8:30PM it began being tracked as an "Invest" area, 91L near 22.0N, 88.6W.

Florida will need to be aware of the potential for Flooding rains, as the system may be offshore in the gulf until
Thursday, driving rain up through the Florida peninsula the entire time. More to come as conditions warrant.

Unlikely, but if a tropical storm forms (best chance for this is Wednesday evening, if at all), it would be named Andrea.

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Storm Surge Tides and Currents for Andrea

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Edited by cieldumort (Thu Jun 06 2013 07:37 AM)

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