Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 4:15 PM GMT on July 31, 2007
Guest blogger Margie Kieper
Tuesday lunchtime update: Because of a busy workload and a sick kitty (Squeak; aka Furball, Metcat), updates today will be minimal, but I'll update with satellite imagery tonight. If you have questions, email them to viewfromthesurface at gmail...and I'll answer them, if I'm able.
The Pacific Ocean is on a roll today.
Invest 99E is continuing to look good this morning, and is likely a TD by now. Update: was designated TD-Eight this afternoon.
Usagi's appearance on satellite continues to improve on IR and water vapor imagery, and the underlying structure continues to improve as well, as this latest of 37gHz microwave images shows, and can be compared with the two others posted earlier in this blog entry:
Usagi's intensity has been increased to 115 kt by JTWC (1-minute max surface windspeed) and 80 kt (10-min wind) by JMA, and it is close to it's maximum intensity, as ocean heat content will steadily lower, between now and landfall in Japan, which should have an impact regardless of the excellent outflow. At the moment, Usagi is a very powerful typhoon.
Regards all the angst on the blog comments yesterday on 99L: Most important is that you will never hear hype from me when blogging about tropical disturbances. Seeing the ocean of dry air ahead of 99L, it was not difficult to have an idea about what was going to happen. Here's something to note: that area just off the South American coast is a kind of a sweet spot. There is always good divergence flowing north that, while it may resemble outflow, is not necessarily indicative of an increase in vorticity. The low level winds are just so, to support a developing low, moisture is drawn from the ITCZ...but many lows associated with a tropical wave that look good there, will fade afterwards when gaining latitude and leaving those conditions behind, especially if moving into a more hostile environment.
It appears the surface circulation of the low associated with Invest 99L opened up or elongated this morning, both on satellite imagery and looking at the earlier QuikSCAT. The dry air is preventing moisture from the ITCZ from making it to the disturbance as it gains latitude, and so it is losing definition. The tropical wave may find a better environment by the time it moves into the western Caribbean or into the East Pacific.
Tuesday morning update: Usagi in the West Pacific continues to steadily strengthen and improve in structure. This morning the eye cleared out, and most recently the structure of the core has become more symmetric. Usagi has been a large, rather sloppy-looking tropical cyclone overall, but don't be fooled by this appearance. As I mentioned yesterday morning, this typhoon should be looking fairly impressive by 00Z 1 August, in about nine hours from this post. Here is a microwave from earlier this morning showing consolidation in the center and continued banding of convection around the center:
There are two other areas being monitored in the West Pacific for possible development.
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In the North Atlantic, as predicted by NHC yesterday, TD-Three has strengthened into Chantal, and strengthening has continued, tilted but clearly tropical, moving rapidly northeast and being pulled into the strong trough coming off the East Coast, spinning furiously like a biker pedaling downhill, on its way to extratropical transition. Life in the fast lane.
Invest 99L underwent a little reorganziation overnight and the mid-level circulation redeveloped in early morning, along with some banding structure. Convection continues to have a hard time sticking due to the dry air, but the low level organization is still intact, so there is some potential to develop into a tropical depression over the next day or so -- but as I said yesterday, chances are that nothing is going to come of this over the next day or so.
More recent morning imagery shows the low level circulation is becoming a little looser, as convection cannot be maintained. It appears this will fall apart as the day progresses.
Finally, there looks to be some potential for development - really, more potential than 99L, as there is quite a lot of energy in this area of disturbed weather - at the tail of the trough coming off the East Coast, east of Georgia and the Carolinas -- but again, a fish spinner.
In the East Pacific, Invest 99E has developed some convection to the southwest of the low level circulation, so that it is no longer an exposed "swirly." A microwave pass from this morning covered enough of the area to show the banding convection and a solid low level structure, so expect this to have potential to develop into a tropical depression as it heads out into the Pacific. Recent visual imagery shows good outflow has started to develop.
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Monday evening update: Convection was able to reform over the center of the exposed low level center of invest 98L tonight, and it has become TD-Three, very near tropical storm strength. It is now centered well north of Bermuda and tracking northeast towards the tip of Newfoundland. The satellite floater is positioned so that the low off the SE coastline can also be observed for development, while TD-Three is rapidly moving north out of the image frame.
Earlier this evening, easterly shear pushed the mid-level circulation and convection right off of the low level center of invest 99L, where it spun off to the west and evaporated, as the low level center continued to move to the northwest, a process that was captured very clearly on the satellite imagery, as seen here on an IR from the NRL web site -- the gray scale helps to determine the height of the clouds:
As I mentioned earlier today, 99L is headed for a large area of dry air. This can be seen on the IR satellite imagery (here, RGB), which I've marked to show the successive surges of the Saharan Air Layer (SAL).
Here a water vapor image clearly shows the extent of the dry air across the Atlantic and eastern Caribbean.
In the West Pacific, Usagi has been steadily strengthening and the eye is starting to become visible on IR and VIS imagery. A microwave from this afternoon shows the solid inner ring of the low level circulation surrounding the eye, partially banded by strong convection (pink).
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Monday Afternoon update: The very nice tropical wave that moved off Africa last Thursday, that is now located at about 50W, has developed rotation and convection and has been designated invest 99L by NHC. While the most recent surge of SAL only extends out to about 40W, most of the tropical North Atlantic and eastern Caribbean remain very dry, so once this wave moves out of the ITCZ and into the eastern Caribbean, chances are that nothing is going to come of it for the next two or three days. The vis loop already shows convection on the northeast and northwest side of the disturbance dissolving as it moves into the dry air.
Convection momentarily burst near the center of 98L, well north of Bermuda and on its way to the middle of the North Atlantic, before getting sheared by the upper level flow.
More on Usagi tonight.
Don't try to adjust that dial: Yes, it does appear that over the past week the NRL TC website has been quietly going berserk. Dalila is done, but keeps coming and going, as do various invests intermittently labeled "Lima" or "Bilis." One could say the site is suffering from Bilis-Lima-ia.
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For Jeff’s early August hurricane outlook, which came out Sunday, link here.
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