Tropical Weather Discussion...Tropical Storm Bonnie makes landfall in South Florida, and has accelerated as expected this morning. It remains poorly organized, and bound for the Gulf of Mexico. It appears the threat of a direct hit to SW Louisiana is a bit less likely today as opposed to this time yesterday, but that being said we need not let our guard down. Now, let's try to figure out where this entity is heading.
Tropical Storm Bonnie Advisory
10a.m. CDT Friday, July 23, 2010
...Small Tropical Storm Bonnie Affecting South Florida...Center will Emerge into the Gulf of Mexico Later Today...
Latitude: 25.4 N
Longitude: 80.3 W
This places the poorly defined center of Tropical Storm Bonnie about 30 miles SSW of Miami, Florida and 130 miles SE of Fort Myers, Florida.
Maximum Sustained Winds: Remain at 40 mph with higher gusts. No significant change in strength is expected in the short-term as the center crosses South Florida, but some slight strengthening is possible once the center emerges into the Gulf of Mexico later today. Tropical storm force winds extend outward to 85 miles from the center, mainly on the East side.
Movement: WNW or 300 degrees @ 18 mph. On this track, Bonnie will move across South Florida and into the Gulf of Mexico later today, and will be approaching the Northern Gulf Coast by late Saturday into Sunday. A general WNW heading is expected to continue through Saturday.
Pressure: 29.77" or 1008 mb.
Watches/Warnings...New Tropical Storm Advisories were issued for the Northern Gulf Coast earlier this morning. The Tropical Storm Watch which had been issued from Morgan City, LA to Destin, FL have been upgraded to Tropical Storm Warnings as of 10a.m. This warning includes Lake Pontchartrain.
A Tropical Storm Warning remains in effect for the Northwestern Bahamas, and for the coast of Florida from Deerfield Beach around through the Florida Keys including Florida Bay and then Northward along the West coast of Florida to Englewood.
A Tropical Storm Watch is in effect for the East Coast of Florida from Deerfield Beach to Jupiter Inlet including Lake Okeechobee.
A Tropical Storm Warning means that Tropical Storm conditions are expected within the warning area generally in about 36 hours. A Tropical Storm Watch means that Tropical Storm conditions are possible within the watch area generally within 48 hours.
Rainfall...Rainfall totals of 1-3" are expected to occur over South Florida, with higher amounts of 5" possible in some locations. Additional rainfall totals in the Bahamas will total 1-2".
Winds...Tropical Storm conditions continue at present over the NW Bahamas, but conditions will improve later today. Tropical Storm force winds mainly in squalls will spread across much of South Florida and the Florida Keys in the warning area today.
Storm Surge...Storm surge levels will rise 1-2' above ground level over South Florida, the Florida Keys and the Bahamas. The storm surge associated with Bonnie will raise water levels 3-5' along and to the right of where the center of circulation makes landfall along the Gulf coast.
Tornadoes...Isolated tornadoes will be possible today over South Florida and the Florida Keys.
Discussion #4...Bonnie is really having a hard time getting her act together. It is still ingesting shear from the ULL out in advance of the system over the Central Gulf. Bonnie has accelerated overnight, and this has caused the storm to catch up to the flow around the ULL once again. Any shot at strengthening is temporarily halted this morning and early this afternoon as the center of circulation has moved inland over South Florida. However, the quick motion of Bonnie will likely keep the system from weakening much while over land either especially given that the area in which the center is traversing is very flat, low marshland. The center of circulation should emerge into the Gulf of Mexico later this afternoon. Sometimes, the center of a poorly organized tropical system will try to re-locate over land. This is a certainly a possibility with Bonnie, and this is certainly being monitored at this time. The center made landfall in Miami-Dade County, and once it emerges into the Gulf a second landfall will be imminent. There are still some questions about where exactly the landfall will occur.
The model suite has been shifting to the right (East) since the storm's inception Thursday. This trend continued overnight, but that being said many of the models are still clustered in Louisiana. A few models still peg landfall for SW Louisiana, but at this time the official track is an average of the model guidance and takes the center inland across SE Louisiana near Grand Isle Sunday. Bonnie has not strengthened since it first became a Tropical Storm Thursday evening, and the environment over which Bonnie will travel in the Gulf of Mexico is not overly favorable for additional development. Yes, water temperatures absolutely support development, but it is the other atmospheric conditions that are only marginally favorable at best. The strong Gulf ULL is the defying factor that is inhibiting intensification. Since, Bonnie has accelerated, strengthening is not likely to occur since it will continue following in the footsteps of the ULL. However, Bonnie's forward progress could slow just a smidge later today into early Saturday as the ULL pulls away and a strong High pressure to the North of Bonnie strengthens and builds further South. Bonnie is being steered by the ULL and around the periphery of the anticyclone to its North. Bonnie is a small tropical cyclone.
Landfall is expected on Sunday somewhere in the Tropical Storm Warning area along the Northern Gulf Coast, this should be between Morgan City, LA and Destin, FL. I will narrow it down further, and say that landfall should be between about Grand Isle, LA and Biloxi, MS. Bonnie is forecast to travel right over the oil spill site, and this leaves many of us with an uneasy feeling. The winds and seas generated by Bonnie will likely churn up the oil slick, and the persistent onshore winds to the right of the center will drive more oil towards the coast. On the left side of the center oil will be pushed away from the coast by strong offshore winds. A storm surge of 3-5' is expected to the right of the center, and this will lead to some coastal flooding and some flooding outside of the hurricane protection levees in SE Louisiana. What about an intensity forecast for landfall? This should not be a major problem at all as far as winds are concerned. Only minimal strengthening is expected if any at all. It is currently forecast to remain a tropical storm until landfall on Sunday. Weakening will occur after that as the system spins down over Louisiana. There is still the chance for further strengthening than is currently forecast if the environment ahead of the storm improves, this seems unlikely at this point. However, I would say it is more likely that Bonnie could fall apart all together, and traverse the Gulf as no more than an open wave due to the largely sheared environment it must traverse. This is forecast by several of our global models, but this is not the official forecast at this point. Either way, this doesn't appear to be a major entity, and it will move in and out very quickly wherever it goes.
Now, what kind of effects can we expect across SW Louisiana based on the current track? We will remain on the dry, subsident side of the storm until well after it makes landfall it would appear. Therefore, we will not have to worry about any storm surge along the coast, and the threat for tornadoes and heavy flooding rains will be much less as well. The tornado threat should be nearly non-existent around these parts if the current projections are correct. The outer rain bands of Bonnie will begin to affect Louisiana on Saturday, and some of these will rotate through the forecast area from time to time through Monday. The chance for more widespread tropical rains across our part of the world will come late Sunday into Monday as the center of circulation spins down over North Louisiana, and the moisture from Bonnie is distributed over a wider area. Depending on the track after landfall, a long fetch onshore flow could develop across the area, putting us in a more favorable area to receive some heavy rain on Monday. This is still subject to more fine tuning as we go along. The bottom line is that rain chances will increase across the area beginning Saturday reaching their highest chance on Monday before conditions improve by Tuesday. Winds will also increase into the 20-30 mph range, but we should have offshore winds based on the current track. I want to reiterate that you should not let your guard down even though it appears we will not experience the most adverse weather from Bonnie. Any shift in the forecast track back to the West will bring the center of circulation closer to our area. I believe we will have a much better idea once Bonnie is in the Gulf later today. Graphics follow.
That's all for this update. The next intermediate advisory by the National Hurricane Center will be issued at 1p.m. (18Z), followed by the next complete advisory at 4p.m. (21Z). My next blog entry will follow the 4p.m. update. Also, look for a regular blog entry later tonight with your weekend forecast, and what to expect from Bonnie across SW Louisiana.
Have a great Friday & God bless!
-DM-
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