Isaac Making Closest Approach to South Florida Later Today

At 11am this morning, Isaac was still a tropical storm, with maximum sustained winds of 65mph. The center of the storm is easily within radar range, and I have a very long loop from Key West showing the passage of multiple rainbands and now the proto-eyewall. A single frame lets you see the center quickly approaching the southern Keys.

This is a relatively large storm, with tropical storm force winds extending 205 miles from the center. A recent visible satellite image puts the size of the storm with its rainbands in perspective.

A detailed hourly forecast from the NWS shows the brunt of the storm will be upon us later this afternoon. Sites in our general area have received 3-5” of rain so far, and could see another few inches before the storm moves away later on Monday. Aside from the danger of flooding, there is a risk of tornadoes associated with hurricanes near/over land.

Isaac will have another couple of days over the warm eastern and central Gulf of Mexico, and will very likely intensify to a hurricane as it travels to the northwest then north toward the north-central Gulf coast. As it looks now, it should make its final landfall somewhere in the north-central Gulf coast as at least a Category 2 hurricane – on the exact 7-year anniversary of Katrina’s infamous landfall. I will continue to watch the situation closely.

Brian McNoldy
Senior Research Associate
& Author of Tropical Atlantic Update
Follow Brian on Twitter: @BMcNoldy

Isaac’s impacts to be felt early next week in South Florida

At 11am this morning, Tropical Storm Isaac’s intensity was increased to 60mph; still a tropical storm, but the strongest it’s been so far. It’s located south of the Dominican Republic and Haiti, and moving toward the west-northwest. The circulation is large, so locations hundreds of miles from the center are experiencing tropical storm conditions. Although, as of this post we are not under a watch, it’s very likely that a tropical storm watch will be issued for us later this evening.

The big two factors of interest to everyone here are wind and rain. The latest tropical storm force wind probabilities for the next five days are shown in this graphic. According to the official forecast from the National Hurricane Center, Miami has a 26% chance of experiencing tropical storm force winds (focused almost entirely between Sunday morning and Monday morning). It is not completely out of the question that we could experience hurricane conditions in that timeframe either… it will depend on how quickly the storm recovers after passing over Cuba. You will notice the weather turning for the worse on Sunday morning, so it would be best to do the bulk of your preparations on Saturday if it still looks like a threat.

And for rain, HPC has predicted about 7-8” of rain for us, but that’s still 2-3 days out, so the exact forecast will change as the storm gets closer and the track is better known. Even 3-4” is a lot of rain, however. I have several radar loops available that will cover Isaac’s path over the next few days to help track the center as well as the outer rainbands. Again, even if the center passes west of the Florida peninsula, we would still feel some effects here, including strong winds and flooding.

To summarize the local aspects, it currently looks like we can expect the rain and stronger winds to pick up on Sunday morning, getting worse throughout the day. Plan for very heavy rain from midday Sunday into midday Monday as well as tropical storm force winds, with a very slight possibility of winds nudging into Category 1 hurricane force range. Conditions should start improving and clearing later on Monday.

Brian McNoldy
Senior Research Associate
& Author of Tropical Atlantic Update
Follow Brian on Twitter: @BMcNoldy

Tropical Storm Isaac Still on Course to Pass by South Florida on Monday

Although Tropical Storm Isaac has weakened just slightly during the past day, any potential impacts on south Florida are still days away and a lot can change.  The storm remains rather disorganized. There are two aircrafts flying into the storm, and both of them have had difficulty finding a coherent center of circulation.  So while it looks ominous on satellite, the structure under those cloud tops is weak – for now.

At 11am this morning, the maximum sustained winds were 40mph, but tropical force winds extended out to 140 miles from the center, which is quite remarkable for a storm this weak. It is forecast to reach hurricane intensity tomorrow before passing over/near Haiti. On this track, it has about one day between leaving Cuba and its closest approach to south Florida, and what the storm does with that one day is a big question mark unfortunately. The latest forecast track as well as watches and warnings are shown here, and the National Hurricane Center website will always have the most current version.

Based on the 11am forecast track, Miami has a 33% chance of experiencing tropical storm force winds within the next five days, and a 2% chance for hurricane-force winds. These numbers will increase as the storm gets closer, but they’re actually fairly high for a 5-day forecast. As it looks now, we’ll start seeing deteriorating weather conditions on Sunday morning, and by Monday morning, the storm should be at its closest approach. Keep in mind that even if the center remains off the west coast of the Florida peninsula, we could still get significant wind and rain over here. My take on the situation would be to prepare for a Category 1 hurricane, and if anything less comes, be thankful.

Have any Hurricane preparedness tips you would like to share? Leave them in the comments.

Brian McNoldy
Senior Research Associate
& Author of Tropical Atlantic Update
Follow Brian on Twitter: @BMcNoldy

Is Isaac Coming to Visit Southern Florida?

Tropical Storm Isaac formed from a strong easterly wave that left the African coast back on August 16th. It became the season’s ninth Tropical Depression this past Tuesday morning, then just twelve hours later was upgraded to the season’s ninth Tropical Storm: Isaac. It has had a history of battling some dry air, which puts a brake on its strengthening, and today is no exception. While it is certainly more robust overall, some vertical shear and dry air are keeping it from getting very strong. As of 2pm this afternoon, the maximum sustained winds were 45mph, and it’s now passing over the island of Guadeloupe in the Leeward Islands.

There are some radar loops of Isaac already available here, and more will be added as it passes by other radar sites. It is also under near-constant reconnaissance by the NOAA and Air Force planes, so any changes in intensity will quickly be assimilated into the National Hurricane Center‘s analysis and forecast.

Model guidance continues to put southern Florida in the cross-hairs on Monday, after passing over Haiti and eastern Cuba. This solution has been consistent for a few days now, with some wobbles back and forth, but generally steady. If this is indeed the case, expect conditions to deteriorate during the day on Sunday, then Monday would be a potential landfall or at least the closest approach. If it doesn’t hit southern Florida head-on, that means it either went a little to the west and would travel up toward the northern Gulf coast, or it went a little east and would travel up toward the Carolinas. Both of those scenarios would give Isaac much more time over warm water to strengthen.

This map shows the cumulative probability of a location experiencing tropical storm force winds within the next five days given the most recent official forecast track. You can see that southern Florida is in the 20-30% bin, and that will increase as the storm gets closer. (The shaded areas on the right part of the image are for Tropical Depression 10, which isn’t going to be a concern.)

As it appears now, regardless of if Isaac hits the Miami area head-on, we can expect some adverse conditions – perhaps tropical storm, and perhaps even hurricane conditions. The exact path over the next 2-3 days will be a big factor in determining what we’ll get here. If the storm passes directly over Hispaniola and some of eastern Cuba, it will be weakened quite a bit. But in the 24 hours it has between Cuba and southern Florida, it could very well re-intensify. It would be prudent to use the next 3-4 days to prepare for the worst and hope for the best.

Brian McNoldy
Senior Research Associate
& Author of Tropical Atlantic Update
Follow Brian on Twitter: @BMcNoldy