Busy Times in the Tropics This Week!

By: Dr. Jeff Masters , 4:15 PM GMT on July 31, 2007

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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 37gHz


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:

Usagi 37gHz


There are two other areas being monitored in the West Pacific for possible development.

* * * * * * *

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.

* * * * * * *

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:

99L sheared


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).

99L and SAL


Here a water vapor image clearly shows the extent of the dry air across the Atlantic and eastern Caribbean.

99L and dry air


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).

Usagi 37gHz


* * * * * * *

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.

* * * * * * *

For Jeff’s early August hurricane outlook, which came out Sunday, link here.

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1149. guygee
3:42 AM GMT on August 01, 2007
Posted By: Ivansvrivr at 2:34 AM GMT on August 01, 2007.
"It seems like the warmer sst.s in august and september would moisten the atmoshphere to the point that moisture would tend to condensate on the sahara dust causing some of it land on the sea surface"

Ivansvrivr - I think that there are at least three problems with the excess dust that inhibits convection.

One is that the dust reflects sunlight back up into the upper atmosphere, thus cooling the surface which helps to suppress convection. The dust layer also absorbs light and longwave radiation from the surface, causing heating in the dust layer.

This is still an area of active research, but another possible consequence of excess dust is that the heated layer above the surface alters the lapse rate and forms an inversion that leads to subsidence, which makes the formation of convection more difficult.

Finally, the are some theories that too many small hygroscopic aerosols in the atmosphere may inhibit the formation of clouds, since the overabundance of condensation nuclei help prevent coalescence into larger water droplets needed for cloud formation. Since there are plenty of salt particles over the ocean to start with, the extra dust may cause something like a "supersaturation" of condensation nuclei, that in combination with the first two factors inhibits cloud formation and convection.

I didn't dig out all the links I have read on this topic, but there are several discussions over on RealClimate, a great place where scientists discuss the scientific literature with lay-folk.

The literature is huge, but also of interest may be the following:
Direct radiative effect of dust on the climate system
Desert dust suppressing precipitation: A possible desertification feedback loop
Subsidence Inversions



Member Since: September 16, 2005 Posts: 0 Comments: 3167
1148. Ivansvrivr
2:34 AM GMT on August 01, 2007
It seems like the warmer sst.s in august and september would moisten the atmoshphere to the point that moisture would tend to condensate on the sahara dust causing some of it land on the sea suface
1147. Ivansvrivr
2:26 AM GMT on August 01, 2007
The thing that worries me about 99l is the mid level half that is farther north. I've had a gut feeling that if 99 got into far northern Carrib. or South Atlantic it would be something serious. Look at Chantel. She was written off but she came to life right afterthe northward turn. I think the warmer SST.s might have made the difference.
1146. pottery2
2:25 AM GMT on August 01, 2007
Thanks NeverPanic. Been watching those for a while too. Fantastic !
1145. pottery2
2:21 AM GMT on August 01, 2007
Katadman. Yes, the SAL will possibly weaken, and will certainly move north. But weaken is not the same as " leave the area completely ".

The SAL never goes completely away, it does blow in different directions though, and is a nuisance in parts of Europe from time to time.
1144. stoormfury
2:18 AM GMT on August 01, 2007
Latest sat pics suggest that the low and mid levels are merging and indications are that 99L is not far from TD4
Member Since: August 22, 2006 Posts: 0 Comments: 2678
1143. NeverPanic
2:17 AM GMT on August 01, 2007
pottery2,
Here is a great link to watch the Dust Storms in N Africa.
Been watching one push off the coast. Most watch the waves but I find these dust storms just as interesting.
Magenta colours show the dust....If you havent seen it...enjoy
here
Member Since: July 29, 2006 Posts: 0 Comments: 834
1142. Ivansvrivr
2:15 AM GMT on August 01, 2007
Dr. Lyons said that Chantel's remnants will become huge low pressure system in North Atlantic. I'm sorry but TWC has gone off the deep end with the global warming mumbo-jumbo. I'm not arguing that climate changes, but we haven't been collecting data long enough yet to know how (if at all) gw is affecting tropics. Some folks think it's all man made. There are others who believe it's other things. Both sides have valid arguements but TWC only shows one side. TWC needs to go back to showing WEATHER!
1141. pottery2
2:14 AM GMT on August 01, 2007
Thats true Kman, and I stress that this is my opinion (obviously )
But it is strange that they stopped using sub- Sahara rainfall figures because there was a lack of co-relation to the formation of storm events. The SAL is a result of dry sub Saharan conditions. Cant be otherwise.
I agree that the SAL has tended to reverse itself, but less and less, generally speaking. There will always be peaks and valleys.
This year could be a repeat of 2004, but I have my doubts about that.

As I said, we all wait to see what happens next !
1140. TropicTopic
2:13 AM GMT on August 01, 2007
my call on 99l tonight..... it has improved in structure greatly in the past 6 hours, even though it is ragged on sat, and now that the circulation center is almost under the convection, has a really good shot at developing. I say...We see continued increased convection with colder cloud tops through the night, the recon kept on schedule and it named a depression tomorrow. Just my opinion.
1139. bellestarr
2:13 AM GMT on August 01, 2007
JJACID...this is what they are watching for...supposed to start 'happening' tomorrow and develop something by Friday....

A weakening front from the northern Gulf of Mexico extending eastward into the Atlantic has been the focus of several areas of thunderstorms pulsing in intensity. While nothing has shown signs of consistent development and there are no immediate concerns, the northern Gulf of Mexico and off the Southeast coast of the United States will need to be monitored.

By AccuWeather.com Expert Senior Meteorologist and Director of Forecasting Operations Ken Reeves

1138. WPBHurricane05
2:13 AM GMT on August 01, 2007
NEW BLOG
Member Since: July 31, 2006 Posts: 56 Comments: 8112
1137. weatherboykris
2:12 AM GMT on August 01, 2007
Posted By: WizardApprentice at 2:08 AM GMT on August 01, 2007.

BREAKING NEWS: 99L has increased intensity to 30 miles per hour



It does not matter.There is no low.Unless one becomes apparent by tomorrow morning,the NHC won't fly,and it will not be named.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
1136. weatherboykris
2:10 AM GMT on August 01, 2007
By August 1st we've seen,on average,20% of all our cyclones.So,if that holds,we'd end up with 15 for the year,which is what it looks like to me right now.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
1135. NormalGuy
2:09 AM GMT on August 01, 2007
okay, thanks, can someone post the latest image of 99l???
1133. weatherboykris
2:08 AM GMT on August 01, 2007
NormalGuy,the convection is increasing,but there is no surface low.It isn't strengthening.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
1132. hurricane23
2:08 AM GMT on August 01, 2007
Pottery as the weeks go by i believe we will see less and less dust out in the tropical atlantic as you can already see signs of that take shape of the african coast.June and july in a normal season represent quite times and personally i wish some folks would understand that.The real season does not really get going till about august 18-20.Tommorow is august 1st and our chances of seeing a named system begin to grow dramatically as the weeks progress.

I see CSU lowering there numbers a bit due to cooler SST'S in parts of the tropical atlantic.A season with 10-14 named systems seems very possible to me.The all important question is how many will affect land.
Member Since: May 14, 2006 Posts: 8 Comments: 13786
1131. katadman
2:08 AM GMT on August 01, 2007
Pottery, Dr. Masters opined last week that the SAL will weaken and move north by the middle of August (if my memory serves me well).
Member Since: September 7, 2006 Posts: 0 Comments: 1081
1130. weatherboykris
2:07 AM GMT on August 01, 2007
No,Kman,it didn't.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
1129. NormalGuy
2:07 AM GMT on August 01, 2007
okay, i was on here an hour ago, and they had 99l at 25mph and now they have it at 30mph? is it getting stronger???
1128. kmanislander
2:06 AM GMT on August 01, 2007
Kris

From looking at the QS pass I would say that it missed where a low center would be ( assuming there is one )
Member Since: August 19, 2006 Posts: 0 Comments: 15816
1127. weatherboykris
2:04 AM GMT on August 01, 2007
99L is not going to form.Looking at the new Quikscat,you can see there's no feature at the surface,not even a wave in the easterlies.The low simply spun down over the day,likely due to the loss of convection and thus upward motion supporting low level convergence.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
1126. msphar
2:04 AM GMT on August 01, 2007
The ambient wind in the tropics is usually about 15 to 20 with gusts to 25. So if this storm is only blowing 30, its not much of an event.
Member Since: August 20, 2006 Posts: 0 Comments: 289
1125. weatherblog
2:03 AM GMT on August 01, 2007
No, Ivansvrivr...nothing new.
Member Since: July 10, 2006 Posts: 27 Comments: 1623
1123. kmanislander
2:03 AM GMT on August 01, 2007
Posted By: pottery2 at 1:56 AM GMT on August 01, 2007.

Any comment on my previous post ??


Hi Pottery, yes a few.

1. Dr Gray and his team gave up using Sub Sahara rainfall in any given year as one of the factors in predicting because they found that there was no longer any verifiable link between the two.

2. Strong SAL in the early season typically reverses itself later in the season and the W Atl has very little now compared to May, June and early July.

3. 2004 saw a dormant start to the season and then for 6 weeks every ingredient for a very active season seemed to fall into place overnight.

It is too early to make any judgments about the rest of the season as 90% is still to come

Just my take on it
Member Since: August 19, 2006 Posts: 0 Comments: 15816
1122. RL3AO
2:03 AM GMT on August 01, 2007
Don't have access to the weather channel updates at :50. PLease let us know what is being said now.

Nothing useful unless you have a headache.
1121. Ivansvrivr
2:02 AM GMT on August 01, 2007
Good Evening evryone. Anything new besides 99 looking like its splitting into two?
1120. pottery2
2:01 AM GMT on August 01, 2007
MonsterHcane. Agreed. But where does the convection come from ?
1119. pottery2
1:59 AM GMT on August 01, 2007
It would be very interesting to see some comparisons of the SAL for August ( for example ) going back 10 years or even better 20 yrs.
1118. louisianaboy444
1:58 AM GMT on August 01, 2007
it looks to be trying to get better organized the thunderstorm action is increasing and it looks as if the low level circulation is trying to get connected with the mid level circulation...if they can get connect and storms can form over them then we can be talking a td but as for now it remains very unorganized
Member Since: August 29, 2006 Posts: 22 Comments: 1352
1116. Miamiweather
1:57 AM GMT on August 01, 2007
hey hurricane you got mail
1115. pottery2
1:56 AM GMT on August 01, 2007
Any comment on my previous post ??
1114. Barbados
1:55 AM GMT on August 01, 2007
Don't have access to the weather channel updates at :50. PLease let us know what is being said now.
Member Since: August 9, 2006 Posts: 0 Comments: 253
1113. louisianaboy444
1:54 AM GMT on August 01, 2007
the only thing lacking for 99L is a large area of deep convection so the mid-level and low-level circulations can get together we will just have to sleep on it and see in the morning!
Member Since: August 29, 2006 Posts: 22 Comments: 1352
1112. RL3AO
1:53 AM GMT on August 01, 2007
BTW, Tropical Storm Erick has arrived.
1111. SevereWeatherFreak
1:53 AM GMT on August 01, 2007
Well g'nite guys. Talk with you all tomorrow.
1110. Drakoen
1:51 AM GMT on August 01, 2007
the LLCD (lower level cloud deck) is nice but the convection still needs to deepen and expand.
Member Since: October 28, 2006 Posts: 57 Comments: 30489
1109. hurricane23
1:51 AM GMT on August 01, 2007
Posted By: jphurricane2006 at 9:47 PM EDT on July 31, 2007. (hide)
adrian that dry air and stable conditions will move lol, it doesnt just sit there.

You have been saying that now for what 2-3 days now LOL...For me i need to see deep concentrated thunderstorm activity through tommorow night before i buy into this disturbance really starting to flurish.
Member Since: May 14, 2006 Posts: 8 Comments: 13786
1108. KEEPEROFTHEGATE (Mod)
1:50 AM GMT on August 01, 2007
no k m its not keep ye'r head up and ye'r eyes wide open
Member Since: July 15, 2006 Posts: 171 Comments: 53809
1107. pottery2
1:50 AM GMT on August 01, 2007
In response to 2 questions __

I think the Atlantic will be hard-pressed this year to produce a significant weather system. My reason for this is that the Sahara Air Layer ( dry air ) shows no signs of going away, and I dont see any reason for it to do so. The Sahara and the western Sahel are bonedry, getting dryer, and expanding south.
The idea that a storm system can form, far less intensify in dry air makes no sense to me.
I'm not a Met, but I've been watching tropical weather a long time, and the above is my humble opinion.

We wait and see, basically.
1106. JJACID
1:49 AM GMT on August 01, 2007
Just my opinion i think 99L will develop. It amazes me the people who write off storms one day then the next day they completely change there tune. What are the steering models set up like? last i looked it took it directly into Central America. I hope they are right and it stays out of the gulf low shear high sst. Only time will tell.
What are they forecasting for the gulf this weekend. Thanks
1105. Bamatracker
1:48 AM GMT on August 01, 2007
no no....dont send anything this way!!!
Member Since: May 17, 2006 Posts: 6 Comments: 1367
1104. JLPR
1:48 AM GMT on August 01, 2007
well time to shut down the laptop i will be back tomorrow on the blog to speak of whatever is on the atlantic
goodnight everyone
:D
Member Since: September 4, 2007 Posts: 36 Comments: 5223
1102. WPBHurricane05
1:48 AM GMT on August 01, 2007
Looking at the water vapor it seems that the dry air has lessen. I say if it can't pull it off tonight, give it one more night, because the dry air might be gone by than.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
1101. kmanislander
1:47 AM GMT on August 01, 2007
Posted By: Bamatracker at 1:44 AM GMT on August 01, 2007.

sorry kman....you'll see 99L before me, make sure and tell it i didnt mean the limp comment.


Will do. Should I pass on your address at the same time ? LOL
Member Since: August 19, 2006 Posts: 0 Comments: 15816
1100. louisianaboy444
1:47 AM GMT on August 01, 2007
theres alot of moisture out ahead of it 23 so that could possibly change we'll just have to wait and see everyone!
Member Since: August 29, 2006 Posts: 22 Comments: 1352

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.