Daweathablog

Charles E. Roop giving his own forecasts, weather discussions, photos and adventures for the Starkville, MS area, Florida, and beyond.

Saturday, August 27, 2011

Irene Makes Landfall

Hurricane Irene made landfall this morning near Cape Lookout, N.C. at 7:30 AM EDT with winds of 85 mph, a category one hurricane, according to the 8 AM advisory from the NHC. The landfall occurred 10-15 miles to the east of were I thought it would be, but it is a little weaker than I expected. I believe the dry air intrusion Friday afternoon and night was mostly to blame for the decrease in intensity. The current intensity, as of 11 AM EDT, is still at 85 mph with a central pressure of 952 mb. The pressure is still hanging around the 950s.

Irene is still expect to make a north-northeast trek and start accelerating in forward speed. It could maintain weak hurricane status until it reenters the Atlantic and move along the New England coastline. The threat remains of some storm surge, especially during high tide, but it shouldn't be as bad as expected. Wind is still a threat, especially in cities with large buildings in close proximity ("wind tunnel" effect could make the winds higher than normal). Inland flooding is also a high risk, especially along rivers and low-lying areas.

For the latest, keep any eye on my Twitter feed.

Friday, August 26, 2011

Irene Update

Well, Floridians can breathe a sigh of relief as Hurricane Irene has and will move north and away from the state's east coast. Irene still had effects on Florida though as rain bands from the western edge of the storm impacted the east coast areas of central and southern Florida. Wind gusts as high as 30 mph were reported in south Florida Thursday afternoon. It's likely that Florida's east coast will continue to encounter heavy surf and a high rip current threat.

Currently, Irene is east-northeast of Jacksonville, Fla. with winds of 100 mph and moving north (360 degrees) at 12 knots. The odd thing is that the central pressure is 951 mb. The winds seem fairly light with relation to the low central pressure. This could be because of a weak high to the east of Irene, which would lead to a lower pressure gradient and, therefore, lighter winds. [Mets: If I am wrong, please chime in on this]. The intensity has decreased a bit from earlier today, likely due to dry air intrusion into the system from the southeast based on water vapor satellite imagery.

I am not expecting too much change in strength through landfall, which is expected sometime tomorrow morning. Models are in agreement of an mid to upper trough to move through the Great Lakes and move east. This, along with Irene being on the western edge of the ridge, should keep Irene moving north - maybe a little more north-northeast - and make landfall along the Outer Banks of North Carolina. Based on the certainty of the models and time to landfall, I am confident that a landfall near Morehead City, NC is likely. I think Irene could still be a category two or strong category one hurricane at landfall Saturday morning. There could be some slight weakening as dry air entrainment could pose a threat to the TC. Shear doesn't seem to be an issue anytime soon as outflow looks really nice.

The concern is that the storm is relatively large and can have impacts far from Irene's center of circulation. Storm surge is still a concern on the coast along with heavy rain to areas that have received plenty recently. Because of the large population centers in New England, the societal impacts of Irene will be great.

NOAA
Since my thesis research falls along the lines of TC and tornado relationships, I should elaborate on a possible tornado threat. Tornadoes from TCs tend to develop on the right-front quadrant of the storm. Literature also points out a higher incidence of TC-tornado outbreaks when dry air entrainment and, therefore, steep relative humidity gradients occur (Curtis 2004). This is something I will try to keep my eye on as the hours move on. For now, the SPC has given a Mesoscale Discussion for the Outer Banks. There is not a high enough risk to issue a severe weather watch at the moment, but the conditions for tornado development could increase later tonight, according to their discussion. Still, with this dry air entering the storm and seeing some decent banding taking place north of the center on visible satellite (see above) has me kind of vigilant.

I will have more on Irene later.

Monday, August 22, 2011

Hurricane Irene Update

A lot has changed in the last couple of days. Tropical Storm Irene came to life Saturday evening as hurricane hunters found a weak circulation and central pressure of 1006 mb. Two days later, it's now a storm that has passed over Puerto Rico and has become the first hurricane of the season. The 8 PM EDT advisory now has Hurricane Irene at category two status with winds of 100 mph and a central pressure of 981 mb.

The last few visible satellite frames show a nice-looking storm. Latest infrared satellite imagery shows Irene continuing to intensify with high cloudtops, mostly around and north of the current center fix (19.7 N 68.7 W).

NOAA
The storm is not moving over the islands (Hispaniola and Cuba) and is not expected to. This leaves the door open to intensification as it moves west-northwest, then northwest as it is expected to encounter a weakness in the ridge over the Atlantic. The guidance models have shifted more east in the last two days, which is a change from where previous runs had Irene hitting Florida Friday into Saturday. Major guidance models - with the GFDL as an exception - have the storm remaining over the waters close to Florida and eyeing the Carolinas for a landfall. The GFDL has been persistant on a Florida landfall and is considered a outlier at the moment.

Southwest Florida Water Management District
As this storm remains over the open waters, my fear is rapid intensification. This is especially the case as Irene reaches the Bahamas. With water temperatures in the low 80s (pushing 85 in some spots), good outflow, no immediate threat of dry air intrusion, and very little shear, I don't see any reason for it not be a category three or four hurricane. This storm has the capability of being a monster TC and needs to be watched.

I've had a lot of friends from Florida ask me about this storm in the last couple of days and, of course, have not been able to give solid answers. With the storm at least five days from Florida and another day or two from the Carolinas, I don't trust the models this far in advance. I think the chances of a Florida impact are lower now, but I wouldn't completely rule it out. People in the NHC cone of error - from south Florida to North Carolina - need to keep an eye on Irene.

I'll post more on this storm in the coming days. Keep tabs on my Twitter account (twitter.com/daweathaman) for the latest.

Friday, August 19, 2011

Watching Invest 97L

It's been a while, but it's a good time for a blog post since the fall semester is now here and the hurricane season is starting to ramp up.

I'll start with something that has been catching eyes in the meteorological community. For the last few days, guidance models have been developing a tropical cyclone (TC) to arrive fairly close to the southeastern U.S. coastline nearly a week from now. On Thursday, the NHC has designated this area of concern as Invest 97L.

NOAA
The vis-sat shows 97L as a decent wave with little shear in the environment. Shear analysis indicates values around 10 kts. Movement has been westerly at nearly 20 mph. Infrared satellite loops show more organization and colder cloudtops in the last few hours. There was some concern of what the Saharan Air Layer (SAL) surrounding 97L would do to it, but it seems that the SAL is not as intense as it was Thursday. It looks as if the wave is doing a good job avoiding dry air intrusions at the moment based on water vapor imagery.

So, what will happen? It's expected to approach the Lesser Antilies on Saturday where conditions could still be favorable for development. Shear is expected to be relatively low. The NHC is giving it a 40 percent chance of development for the next 48 hours. I'm confident that the chances will increase, at least through Saturday. Guidance models are in fair agreement of 97L moving toward the west-northwest and getting close to Puerto Rico and Hispaniola at the beginning of next week. What happens beyond that is iffy...

Path...
The system would eventually take a more northerly path. The GFS, at this moment, has the storm hitting the western side of Florida and striking the Big Bend next weekend. The Euro has the storm hitting the southeastern coast of Florida and moving north-northeast to northeast a day later than the GFS. It would depend on a) how strong the ridge to the east is and b) any troughs in the eastern U.S. to help "pick up" the storm. For example, the GFS seems to have the Bermuda High fairly strong and keep it more west than the Euro. Other models don't go this far out.

Strength...
If 97L / future TC moves over the islands (Hispaniola, Cuba), they can have an effect on further development of the system and even decrease its strength. The mountainous terrain can do some damage to a healthy TC. If the wave / TC doesn't cross the islands as much, it may not lose so much strength. It all goes back to the path of the storm, which is still highly uncertain.

Nutshell...
When I start to see consistant patterns in a guidance model (run-to-run) and the guidance models agreeing with each other, my eyes start to get wider. Still, I have a hard time trusting guidance models beyond three or four days. I'm not comfortable making calls this early in the game. My advice: People from the Carolinas to Brownsville, TX need to watch the tropics for the next week. Things might get interesting.