Tropical Weather Discussion...Disorganized Bonnie weakens a bit back to a Tropical Depression as she gets ready to emerge into the Gulf of Mexico. The forecast track continues to shift Eastward, and the prognosticates a weak system all the way until landfall. The fast forward speed continues, and the threat to SW Louisiana continues to decrease.
Tropical Depression Bonnie Advisory
4p.m. CDT Friday, July 23, 2010
...Bonnie continues to struggle with plenty of wind shear wrapping into the storm...Northern Gulf Coast under the gun for a heavy rain threat by late in the weekend...
Latitude: 26.2 N
Longitude: 81.9 W
This is 35 miles S of Fort Myers, Florida and 485 miles ESE of the Mouth of the Mississippi River.
Maximum Sustained Winds: 35 mph w/ higher gusts. Bonnie is now a tropical depression, but it could retain tropical storm status at some point over the Gulf of Mexico later tonight or on Saturday. Bonnie should remain a weak tropical entity through landfall.
Movement: Bonnie continues to move quickly. It is currently heading to the WNW or 300 degrees at 18 mph. This motion will continue for the next day or so, before some reduction in forward speed and a gradual turn toward the North occurs as well. On this track, Bonnie will move away from Florida into the Gulf of Mexico this evening, and will approach the Northern Gulf of Mexico coast late Saturday into Sunday.
Pressure: 29.80" or 1009 mb.
Watches/Warnings...All watches and warnings for the Bahamas, South Florida, and the Florida Keys have been discontinued. The Tropical Storm Watch for Lake Okeechobee has also been discontinued. The Tropical Storm Warning remains in effect for the Northern Gulf of Mexico Coast from Morgan City, LA to Destin, FL.
A Tropical Storm Warning means that Tropical Storm conditions are expected within the warning area generally in about 36 hours.
Rainfall...Bonnie will likely produce rainfall amounts of 1-3" across SE Louisiana, Southern Mississippi, Southern Alabama, and the Extreme Western Florida Panhandle. Isolated amounts up to 5" are possible in this area. An additional 1-2" of rain is expected across Central and Southern Florida through tonight.
Wind...Wind impacts will be minimal. Winds to tropical storm force mainly in squalls will gradually abate over South Florida, and conditions there will improve tonight. Conditions will begin deteriorating across the Northern Gulf Coast on Saturday with tropical squalls moving onshore by Saturday afternoon. Occasional tropical storm force winds will be possible in this area as the system moves onshore late Saturday night or early Sunday. The strongest winds will be confined to the immediate coastline.
Storm surge...Storm surge levels will rise by as much as 3-5' along and to the right of where the center makes landfall along the Northern Gulf Coast.
Discussion #5...The discussions will be getting shorter and shorter now as we are getting a much better idea of what will happen with little Ms. Bonnie. The very disorganized storm has weakened back to a Tropical Depression likely due to the interaction with South Florida and the large amount of shear that is ingesting dry air into the system. This is a small storm, and it doesn't have that classic tropical system appearance at all. Because of the shear, the storm is really more elongated than anything, and takes on more of an oval shape as opposed to being completely symmetric. The center of circulation is still exposed from the deep convection, and it is on the SE flank of the storm. Most of the deepest convection is actually on the NW side of the circulation at this time. This is clearly another sign of the disorganized nature of the storm.
The forecast track continues to shift to the East, and landfall could very well end up being in coastal Mississippi. Currently, the forecast track shows landfall in extreme SE Louisiana around Slidell, coming up through the Gulf over the Rigolets. This track would also be better news for the oil spill in the Gulf. This would keep an offshore flow in place across much of the oil spill zone. This would help drive oil away from the coast, and the choppy seas may also help to disperse some of the oil, to take it easier to clean up when operations resume. Of course, there is still much uncertainty with respect to this, and we're all waiting on pins and needles to see what will happen. Now, those areas to the right of the center will certainly see a persistent onshore flow develop with tropical storm conditions (winds 40-50 mph), and that in turn will drive oil closer to the coastline in those areas. The storm itself will not really be a big deal, as many of our typical afternoon thunderstorms this time of year can be stronger than Bonnie currently is. Rainfall will be the main land impact. If the current structure of the storm remains the same, then the heavier rainfall could actually be closer to SW Louisiana than you would typically expect with a tropical system.
There is no reason to believe that the conditions for significant strengthening will develop. The large ULL currently to the South of Louisiana will continue to be the driving force and steering mechanism for Bonnie. Since Bonnie has accelerated today, it has remained too close to the ULL to have any chance to take advantage of somewhat more favorable conditions. Of course, its interaction with land over South Florida also helped to weaken it today as I said earlier. Even though it is emerging into the Gulf now, that doesn't always mean strengthening will occur. The environmental conditions usually dictate what can and will happen with a storm. This time, since Bonnie is already so disorganized, there is some question as to whether Bonnie can even survive despite traveling over the warm waters of the Gulf of Mexico. The official forecast calls for subtle re-strengthening into a minimal tropical storm before landfall. However, I believe it is becoming more likely that Bonnie will not survive on its trek through the Gulf. It could very well just make landfall as an open wave, and just bring an increase in rainfall for a few days across the state. I will go with the official forecast from the National Hurricane Center for now, although I do speculate that degeneration may occur within the next 24 hours. The steering currents are quite strong, and Bonnie will certainly continue on its WNW track and come very close to the Bayou State by Sunday morning. Whatever state Bonnie is in as it moves into the state, it will begin to spin down over land Sunday into Monday with the circulation moving into North Louisiana Monday. Enhanced moisture should encompass the state through Tuesday or Wednesday as the remnants of Bonnie slow down to our North and open up the Gulf for a long fetch onshore flow to become established across the state.
That's all for now. Enjoy your evening! The next intermediate advisory from the NHC will be issued at 7p.m. followed by the next complete update at 10p.m. My next update will come shortly after 10p.m. tonight as the new information from the Hurricane Center becomes available. I will also post a fresh regular forecast discussion so you will know exactly what to expect for the weekend and early next week until we get Bonnie out of the way.
Have a good Friday evening & God Bless!
-DM-
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