 |
| Author | Post |
|---|
admin
Administrator
| Joined: | Sat Dec 23rd, 2006 |
| Location: | |
| Posts: | 2565 |
| Status: |
Offline
|
|
Posted: Fri Aug 29th, 2008 04:19 pm |
|
Posted by: JeffMasters, 11:20 AM EDT on August 29, 2008
Tropical Storm Hanna
Tropical Storm Hanna is beginning to get its act together. The upper level low to Hanna's west has weakened some and moved away, allowing Hanna to position its center of circulation underneath its heaviest thunderstorm activity. Visible satellite loops show that the amount and intensity of heavy thunderstorm activity has increased considerably, and there are now two prominent upper-level outflow channels visible, on the north and east sides. Strong upper-level winds from the upper-level low to Hanna's west are still interfering with the thunderstorm development and upper-level outflow on Hanna's west side. Radar out of Martinique shows a large area of heavy thunderstorms that are poorly organized (no spiral bands). This morning's QuikSCAT pass saw winds of 40-55 mph at the surface. The first Hurricane Hunter mission for Hanna is scheduled for Sunday.
The forecast for Hanna
Steering currents imparted by the counterclockwise flow around the upper-level low to its west will keep Hanna moving northwest, to a point midway between Bermuda and the Bahama Islands. About 3-4 days from now, a strong blocking ridge of high pressure is forecast by most of the models to build over Hanna, forcing it to the southwest towards the Bahamas. This is an unusual motion for a hurricane, and it would be surprise to see Hanna move as far south as some of the models are predicting--all the way into Cuba. However, the Bahamas are at high risk from this storm 4-5 days from now. Hanna may be weakening at that time, as wind shear from an upper-level trough to the north of the storm is expected to bring 15-25 knots of shear to the storm. In the longer term, both the ECMWF and GFS models are predicting Hanna will pass through South Florida or the Florida Keys into the Gulf of Mexico by Thursday or Friday next week.
A major complicating factor in forecasting both Hanna's track and intensity may be the possible development of a tropical disturbance behind it, near 18N 41W (see discussion below, under "Elsewhere in the tropics". This disturbance is forecast to develop into a tropical storm 3-5 days from now by some of the models. If so, the new storm could substantially alter the path and strength of Hanna. Don't believe that Hanna will be going through South Florida quite yet; the models do very poorly with hurricane-hurricane interactions, and the long term fate of Hanna is still highly uncertain.
Elsewhere in the tropics
A large circulation is located near 18N, 41W, in the mid-Atlantic Ocean. This morning's QuikSCAT pass show an elongated, poorly formed circulation, with top winds of 25 mph. Heavy thunderstorm activity has increased since yesterday, but the disturbance is battling marginal wind shear of 15-20 knots and dry air on its south side. Wind shear is expected to stay marginal for development over the next few days, limiting this system to only slow development. NHC is giving this system a low (<20% chance) of developing into a tropical depression by Sunday. Some slow development is possible over the next few days, but the system has a better chance 3-5 days from now, when its environment will be moister. Several of the models develop it, and predict the system will be 500 miles or so north of the northern Lesser Antilles Islands by Monday or Tuesday.
Cape Verdes Islands disturbance, 97L
A low pressure system (97L) with a large circulation and plenty of spin emerged from the coast of Africa last night, and is now located near 13N 19W, a few hundred miles southeast of the Cape Verde Islands. This morning's QuikSCAT pass revealed a closed surface circulation and top winds of 25 mph. This system is already developing some concentrated heavy thunderstorms over the waters south of the Cape Verde Islands. Wind shear is a moderate 10-15 knots over the storm, and is expected to remain in the low to moderate range the next few days. NHC has given this system a medium (20%-50%) chance of developing into a tropical depression by Sunday. The models have been very aggressive developing this system over the past few days. It is too early to speculate whether this storm might end up recurving out to sea or not.
There are two other impressive African tropical waves lined up behind 97L that are also likely to be a threat to develop once they move offshore Africa next week. The long-range GFS model develops all three of these waves.
Disturbance 96L in the Bay of Campeche
Some good news: the blob in the southern Gulf of Mexico, in Mexico's Bay of Campeche, dissipated last night.
My next blog will be by 5pm this afternoon.
Jeff Masters
____________________
Life is short. Break the rules, Forgive quickly, Love truly, Laugh uncontrollably,
and never regret anything that made you smile!
|
admin
Administrator
| Joined: | Sat Dec 23rd, 2006 |
| Location: | |
| Posts: | 2565 |
| Status: |
Offline
|
|
Posted: Sat Aug 30th, 2008 11:49 am |
|
not a pretty picture of Gustav and Hanna so close to each other.....
Attachment: Picture 10.png (Downloaded 21 times)
____________________
Life is short. Break the rules, Forgive quickly, Love truly, Laugh uncontrollably,
and never regret anything that made you smile!
|
Current time is 12:21 pm | |
|
|
|
|
