The Latest on Tropical Storm Bonnie...

Thursday, July 22, 2010

Tropical Weather Discussion...Virtually no change to report here on the latest update on Tropical Storm Bonnie. Some restructuring or re-organization of the low-level center is still ongoing, and the National Hurricane Center has left everything virtually unchanged with respect to the intensity and the official forecast track. Some slow strengthening is expected through Friday as Bonnie shoots across the Florida Keys and through the Florida Straits. She is bound for the Gulf, but how strong will she be and where will she wind ultimately wind up? Those are the questions we need to answer tonight.

Tropical Storm Bonnie Advisory

10p.m. Thursday, July 22, 2010

Latitude: 23.4 N

Longitude: 76.5 W

The places the low-level center of Bonnie about 125 miles SSE of Nassau, Bahamas and 285 miles SE of Miami, Florida.

Maximum Sustained Winds remain near 40 mph w/ higher gusts. Some slow strengthening is expected through Friday, and Bonnie should cross the Florida Keys as a tropical storm on Friday before emerging into the SE Gulf of Mexico Friday night. Tropical storm force winds extend outward to 45 miles from the center mainly to the NE.

Movement: NW or 305 degrees @ 14 mph. This general motion should continue overnight, but a gradual increase in forward speed, and a motion to the WNW should begin on Friday. On the current forecast track, Bonnie will pass near or over the Florida Keys and South Florida Friday, and move into the SE Gulf of Mexico Friday night into Saturday.

Pressure: 29.74" or 1007 mb.

Watches/Warnings...There has been some modifications/revisions to the watches and warnings that had been issued previously. A Tropical Storm Warning has been issued for the East Coast of Florida from Golden Beach to Deerfield Beach. A Tropical Storm Warning has been issued for the West Coast of Florida from Bonita Beach to Englewood.

A Tropical Storm Warning is effect from Englewood, Florida around to the East Coast of Florida up to Deerfield Beach. This includes the Florida Keys and Florida Bay.

A Tropical Storm Watch is in effect from Deerfield Beach to Jupiter Inlet on the East Coast of Florida. This includes Lake Okeechobee.

The Tropical Storm Warning for the Central and Northwestern Bahamas remains in effect.

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.

All interests along the Northern Gulf Coast should continue to monitor the progress of Bonnie. Additional watches may be required for a portion of the Northern Gulf Coast on Friday.

Rainfall...Rainfall totals of 2-4" are expected to occur over South Florida, with higher amounts of 4-6" possible in some locations. Rainfall totals of 3-5" are expected over the Bahamas, with higher totals up to near 7" expected in isolated locales.

Winds...Winds near Tropical Storm force will spread over the Central and Northwestern Bahamas tonight and Friday, and into South Florida on Friday.Conditions will deteriorate over South Florida beginning late tonight.

Storm Surge...Storm surge levels will rise 1-2' above ground level over South Florida, the Florida Keys and the Bahamas.

Discussion #3...There is not much in the way of new information to report tonight. The storm is still in its formative stages. This means that center fixes or re-location are possible through Friday. The storm looks very ragged on satellite depictions tonight. One might question that it is still even worthy of being a tropical storm as of this writing, but for the sake of the official forecast we'll run with it. Bonnie is approaching South Florida and the Florida Keys tonight. Squally weather is encompassing portions of the Bahamas with rain bands spreading through the Miami area down into the Keys. The upper level low that has created a shear environment in its wake over Bonnie continues to play in role in the present state of things. This significant ULL could also lead to further ramifications with Bonnie. Bonnie should follow closely on the heels of the ULL. Models don't indicate any robust development, and most keep it no stronger than a tropical storms. There are some outliers which decay the storm into an open wave over the SE Gulf of Mexico, while others swing the other way and suggest Bonnie will reach hurricane status before landfall. A split of these two ideas seems logical, thus the forecast philosophy that Bonnie will remain a tropical storm over the warm waters of the Gulf.

The water temps over this region certainly are more than adequate to support storm maturation. However, the storm should not strengthen a whole lot, due to the ongoing hostile conditions which are expected to continue into the weekend. Thus, only a very modest intensification is expected until landfall late in the weekend. Bonnie is being steered around the Western periphery of the strong Bermuda high to its North. The high should continue to help steer Bonnie, and the steering currents will actually support a storm that should increase its forward speed as the high strengthens and builds a bit further West into the Mississippi Valley. The low-level center has been trying to re-position itself underneath the deep convection, but so far this has not occurred due to the shear environment that currently exists over the top of Bonnie. If the center can ultimately co-exist underneath the deepest convection, then the chances for a more steady strengthening will increase. Right now, it seems as though the shear that is present will remain in place, therefore not allowing Bonnie to take advantage of the very conducive SSTs in place over the Gulf waters. The official forecast has been nudged a bit to the right (East) of the previous forecast, mostly based on the fact that the center has relocated further North tonight. The models are still in very good agreement of a landfall somewhere on the Louisiana coast in the Sunday-Monday time frame.

As of right now, the official forecast track lessens the threat of a direct hit to SW Louisiana, however, we are certainly not off the hook, and the forecast track can certainly be shifted back to the West in future forecasts. The 10p.m. forecast track takes the storm inland Sunday afternoon as a 50 mph system close to Houma, and then tracking up to near Baton Rouge, and decaying near Monroe Monday night into Tuesday. There is still much uncertainty in the eventual track, despite the good agreement from the models. Further center fixes and wobbles by the storm can affect the official track one way or the other. Also, if the aforementioned ridge is stronger or weaker than expected than the track can shift further West or East again. It all depends on the synoptic features in place out ahead of Bonnie. The ULL will also likely continue to be a factor. Certainly, in the short-term this feature will cause shear to inhibit much development, but some models suggests the shear will relax as Bonnie enters the Gulf, and this could provide for a better opportunity to strengthen. However, the flow carved up by the ULL could actually carry Bonnie on a similar track to the West. That's why everyone from the Upper Texas Coast to the Florida Panhandle needs to keep a close eye on Bonnie. I believe the eventual track of Bonnie will be more cut and dry in about 24 hours when Bonnie has emerged into the Gulf. The intensity forecast laid out by the National Hurricane Center seems feasible as well. I really don't see Bonnie having the opportunity to undergo a period of rapid intensification due to the shear over the Gulf, and its fairly quick motion.

It's basically a crapshoot with respect to how strong Bonnie could be in the Gulf. There is the possibility that Bonnie will degenerate and become an open wave if the shear increases again, or it could reach minimal hurricane status (category 1) if the shear relaxes, and the environmental conditions ahead of Bonnie become more favorable for development. The idea that Bonnie's intensity will be somewhere in the middle of these two solutions is conceivable, and I see no reason to deviate from the National Hurricane Center's forecast. Landfall should come sometime Sunday afternoon or Sunday night on the Louisiana coastline. It could be early Monday if the system is closer to Lake Charles, this again all remains to be seen. The most adverse weather conditions will lie along and to the right (East) of the center of circulation. Storm surge levels of 3-4' will be possible along the coast along with much higher seas and winds. Winds gusting into tropical storm force range should be expected for much of the area from I-10 southward to the East of the center. Heavy rain and isolated tornadoes will be the main issues. The tornado threat will be realized on the right-hand side of the circulation only. Where this is exactly of course remains to be seen. If you base it on the current track, all of the nasty weather would be along the Mississippi River and points Eastward including Baton Rouge and New Orleans, and the weather across SW Louisiana would be limited to just a few squalls on the periphery of the storm. A shift back to the left would bring the threat of the most serious weather back into SW Louisiana, so the word to the wise here is to stay on top of the weather situation. Have a plan in place should tropical storm conditions be expected across the forecast area. Tropical Storm Watches will likely be issued for the Louisiana coastline on Friday. Undoubtedly, the worst conditions with Bonnie will be felt along the coast, and the main impacts inland will be the heavy rain and flooding threat and the tornado threat. There is also the oil spill to contend with. Bonnie is forecast to track right over the oil spill zone on Saturday. This has already caused clean up operations to cease, and it is still uncertain as to how this will affect the oil slick. Even though this should be a weak system, it will still be strong enough to cause some issues with the oil...just have to wait and see! As Bonnie gets into the Gulf, much of the future forecasts will become clearer. Stay tuned!

That's all for this update. The National Hurricane Center will issue the next intermediate advisory at 1a.m. Friday, followed by the next complete advisory at 4a.m. Friday. My next update on Bonnie will come after the 10a.m. update Friday morning. Have to sleep some now, because I might not be sleeping at all once the storm is nearing the coast. The regular forecast discussion will be posted shortly just above this post. Thanks for reading, and be sure to check back in the morning for all the latest on Bonnie.


Have a great Thursday Night & God Bless!
-DM-