TD 8? Not yet...

By: Dr. Jeff Masters , 4:05 PM GMT on July 29, 2005

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Satellite imagery of the tropical wave approaching Puerto Rico shows a less impressive system than yesterday. The wave covers less area, has reduced upper level outflow, and is battling increased wind shear. However, the dry air on the wave's west side that was inhibiting thunderstorm development last night is less apparent on today's water vapor satellite imagery.

The most most impressive sign of organization of this wave is in the pressure falls observed over the Lesser Antilles islands this morning. A plot of the past week's pressures at one of our personal weather stations in Anguilla, an island in the northern Lesser Antilles about 150 miles east of Puerto Rico, shows a significant pressure fall this morning:



Keep in mind that it is a bit tricky to interpret pressure readings in the tropics. The pressure plot shows a curious regular oscillation with amplitude 1 mb, and a peak twice per day at about 11am and 11pm local time. This oscillation is due to the presence of atmospheric tides in the atmosphere. Like tides in the ocean, atmospheric tides move as a wave around the planet with a very regular period in sync with the Earth's rotation rate. The atmospheric tides we see in the Anguilla data are primarilly due to solar heating of the atmosphere. When the sun rises and starts heating the air, the air expands in response, lowering the pressure in the vicinity, and pushing a wave alternating high and low pressure air all the way around the globe. The amplitude of this wave is highest--about 1.5 mb--where the sun's heating is greatest, near the equator. The wave's minimum amplitude of about 0.5 mb occurs near the poles. The period of the wave is 12 hours.

Mentally remove the wriggles from the pressure plot above, and you can see that the drop in pressure this morning in Anguilla was not due just to the atmospheric tidal effect, but must also have had a component due to a low pressure system moving in. Similar pressure falls are being observed on nearby islands that the tropical wave is affecting, such as St. Maarten.

A hurricane hunter aircraft will investigate the area at 4pm today to see if a tropical depression is forming. If a depression does form, its potential track is highly uncertain. The GFS model maintains that it will track WNW and threaten the East Coast, while the ECMWF has the system moving into the Gulf of Mexico. The GFDL model moves the system into the Bahamas and disipates it in 36 hours. In any case, if a depression does form, it will have some significant barriers to overcome in order to intensify. If the storm moves north, there is a large upper-level trough with strong shearing winds to contend with. If the storm stays further south, interaction with the land masses of Puerto Rico and Hispanolia will hinder it.

Dr. Jeff Masters

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164. WillJax
5:10 AM GMT on September 29, 2005
New Blog?
Member Since: September 7, 2005 Posts: 0 Comments: 33
163. Alec
3:54 AM GMT on July 30, 2005
im in the new blog now.
162. Alec
3:18 AM GMT on July 30, 2005
hi everyone!
160. weatherboyfsu
12:35 AM GMT on July 30, 2005
Hey stormtop....im still collecting predictions for the total season.....
Member Since: July 17, 2005 Posts: 0 Comments: 1025
159. weatherboyfsu
12:33 AM GMT on July 30, 2005
whats up.....fill me in on the lastest....i looked at the lastest satellite loops....dont see anything....
Member Since: July 17, 2005 Posts: 0 Comments: 1025
158. Toyotaman
11:16 PM GMT on July 29, 2005
Last message to Stormtop of course.
157. Toyotaman
11:13 PM GMT on July 29, 2005
i'm sorry, but I find it very hard to believe that you have been studying hurricanes for the past 30 years. Me thinks that you are a teenager judging by your temperment.
155. Toyotaman
11:08 PM GMT on July 29, 2005
"hawk this will be harvey today if not right this minute when the recon plane goes and checks it out...the clear center is at 17.5 63.5...if you cant see it you are only fooling yourself."

Stormtop, do you remeber saying this earlier this morning on the other blog? This means that you did predict it to be a named storm today. Quit changing your story.
154. HurricaneKing
11:02 PM GMT on July 29, 2005
But first Florida
Member Since: July 6, 2005 Posts: 71 Comments: 2487
153. HurricaneKing
11:02 PM GMT on July 29, 2005
I predict it will hit North Carolina.
Member Since: July 6, 2005 Posts: 71 Comments: 2487
151. WSI
10:54 PM GMT on July 29, 2005
The depression isn't there yet. Whoever predicted it would be there when the plane flew in was wrong.
150. Denials
10:27 PM GMT on July 29, 2005
stormtop,

You said "i will gurantee it will be a TD 8 when the plane gets down there ..it may even be harvey"

Stormtop,

You got it wrong. The data from the plane is back, and there's no tropical depression yet.

Will you admit that you are wrong?
149. outrocket
10:27 PM GMT on July 29, 2005
hurricane watcher,are basing direction on the idea that the bermuda high will re-establis it's self afte upper low clears bahama's..If so you may be right ,that could keep this wave farther south.
Member Since: July 15, 2005 Posts: 104 Comments: 11011
148. STORMTOP
10:17 PM GMT on July 29, 2005
we will see toyota......you dont plkan on doing smething to the atmosphere do you?i dont trust you toyota...you have to be watched closely....lol
145. Toyotaman
10:13 PM GMT on July 29, 2005
No need to shout Storntop, I did reread your post and you guarenteed that it would be a depression and possibly a storm. Well its not either. You also said that there would be 3 named storms by the end of the month, right? Only 2 days left my friend.
142. outrocket
10:05 PM GMT on July 29, 2005
ever feel like this was an improv and we are mearly waiting for godot?
Member Since: July 15, 2005 Posts: 104 Comments: 11011
140. Dragoon
10:00 PM GMT on July 29, 2005
This system looks similar in organization to the system that spawned TS Gert. Judging from the satellite appearance over the past few hours.. it does appear that the storms are trying to get better organized.. and perhaps even that a convective band is trying to consolidate to the northeast of the weak low. If this trend continues it would actually not surprise me to see a depression form sometime later tonight.
139. Hawkeyewx
9:56 PM GMT on July 29, 2005
Unless there is a big blowup of convection over the would-be center in the next few hours it is highly unlikely this thing will be called a TD before tomorrow.
Member Since: July 5, 2005 Posts: 2 Comments: 1924
137. STORMTOP
9:44 PM GMT on July 29, 2005
lol ok turtle i dont change my opinion on waht i say..i said 8pm and this is not a conspiracy and im sticking to it i dont hedge 3 hours...what is the difference if its a td at 8pm it will be a td at 11pm...
135. turtlehurricane
9:42 PM GMT on July 29, 2005
goodbye
Member Since: July 22, 2005 Posts: 227 Comments: 469
134. turtlehurricane
9:41 PM GMT on July 29, 2005
ok stormtrop, i didnt say it was impossible, just facts have forced me to change my opinion
Member Since: July 22, 2005 Posts: 227 Comments: 469
133. turtlehurricane
9:40 PM GMT on July 29, 2005
i agree
Member Since: July 22, 2005 Posts: 227 Comments: 469
132. STORMTOP
9:40 PM GMT on July 29, 2005
comment you made turtle was 8pm agreeing with me..if you have amnesia scroll up you will see what you said...lol
131. Hawkeyewx
9:39 PM GMT on July 29, 2005
turtle, this system definitely needs a big blowup of deep convection over the center-to-be, and it needs the convection to maintain itself rather than quickly diminish like it has been doing up to this point
Member Since: July 5, 2005 Posts: 2 Comments: 1924
130. STORMTOP
9:38 PM GMT on July 29, 2005
ok hawk now the nhc know what time i want them to drop the bomb on everyone in here lol......this is to funny.
129. turtlehurricane
9:36 PM GMT on July 29, 2005
stormtrop it is possible, maybe at 11pm. I say 11pm because they want to wait and make sure if anything happens that it is actually gonna hold. Speaking of that thunderstorm activity is increasing alot over the storm. Any comments?
Member Since: July 22, 2005 Posts: 227 Comments: 469
128. STORMTOP
9:34 PM GMT on July 29, 2005
lol@ hawk
127. STORMTOP
9:33 PM GMT on July 29, 2005
you read my post turtle do i have to repeat myself..i said you wont hear anything until 8pm tonight in a special advisory..i believe you agreed if you scroll up you will see what im talking about.
126. turtlehurricane
9:32 PM GMT on July 29, 2005
all it takes is one good flare of convection to classify this thing.maybe at the diurnal maximum.
Member Since: July 22, 2005 Posts: 227 Comments: 469
125. Hawkeyewx
9:30 PM GMT on July 29, 2005
Don't buy it, Stormtop, the NHC is involved in an effort to discredit you. Their recon plane actually did find TS Harvey, but they are intentionall keeping that info from you.
Member Since: July 5, 2005 Posts: 2 Comments: 1924
124. STORMTOP
9:27 PM GMT on July 29, 2005
lol toyota you cant read posts i did not call it a tropical storm..WHAT I SAID WAS SORRY FOR THE CAPS BUT I THINK HE NEEDS THIS...I SAID I WOULDNT BE SURPRISE IF THEY FOUNGD HARVEY WHEN THEY WENT DOWN THERE..I DIDNT SAY IT WAS A TROPICAL STORM BUT I DID SAY IT WAS A DEPRESSION..YOU GOT IT NOW?
123. turtlehurricane
9:26 PM GMT on July 29, 2005
there is a low after all but, weak
Member Since: July 22, 2005 Posts: 227 Comments: 469
122. turtlehurricane
9:25 PM GMT on July 29, 2005
ok, its close but not a depression.....any comments Stormtrop?
Member Since: July 22, 2005 Posts: 227 Comments: 469
121. isobar5
9:24 PM GMT on July 29, 2005
Thanks.
120. turtlehurricane
9:24 PM GMT on July 29, 2005
Data from an Air Force Reserve unit reconnaissance aircraft...
satellite images...surface observations...and San Juan Doppler
radar data indicate the low pressure area associated with a strong
tropical wave moving through the northern Leeward Islands has not
yet organized enough to be classified as a tropical depression.
However...conditions appear somewhat favorable for a tropical
depression to form later tonight or Saturday over the extreme
northeastern Caribbean Sea and in the vicinity of Puerto Rico and
surrounding islands. Another reconnaissance aircraft is scheduled
to investigate the system tomorrow. Squalls producing brief periods
of heavy rainfall and gusty winds to near tropical storm force...
especially over higher terrain...could occur over the northern
Leeward Islands...the Virgin Islands...and Puerto Rico tonight...
and over Puerto Rico and Hispaniola on Saturday. Interests near
this area should closely monitor the progress of this system.
Member Since: July 22, 2005 Posts: 227 Comments: 469
119. STORMTOP
9:23 PM GMT on July 29, 2005
yes i have lots of comments on that i made it this morning..i am worried about it and its sitting over the gulf stream...i saw convection fire up over it earlier and then died down..but to answer your question yes you should not write it off isobar let me know if you see the convection increase...good call..
118. turtlehurricane
9:22 PM GMT on July 29, 2005
isobar, looks like the remnants of a mesoscale complex, not much to worry about unless it flares, which it probably won't
Member Since: July 22, 2005 Posts: 227 Comments: 469
117. turtlehurricane
9:21 PM GMT on July 29, 2005
well that is the movement of the storm but, lets not argue, if it is this hard to see a circulation it must be weak if it exists
Member Since: July 22, 2005 Posts: 227 Comments: 469
116. Toyotaman
9:20 PM GMT on July 29, 2005
Stormtop, you keep asking if every has a plane but you have already called it a tropical storm. How did your plane or boat for that matter do?
115. Toyotaman
9:18 PM GMT on July 29, 2005
Look real close, nothing is moving south, east, or north. Its all moving either wnw or sw. That does not make a closed low. T-storms in my area almost always go in different direction.
114. turtlehurricane
9:18 PM GMT on July 29, 2005
yes the showers near St.Croix but, you have to look around those to see that there is a circulation.
Member Since: July 22, 2005 Posts: 227 Comments: 469

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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.

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