Subtropical Depression 17 forms; monsoon rains kill over 100 in Asia

By: Dr. Jeff Masters , 1:04 PM GMT on October 06, 2010

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Subtropical Depression Seventeen formed this morning, approximately 200 miles north of Puerto Rico. The storm is not a threat to bring high winds to any land areas, but will produce heavy rains over Puerto Rico, the Virgin Islands, the northern Lesser Antilles, and perhaps the eastern Dominican Republic. Radar estimated rainfall over Puerto Rico and the Virgin Islands (Figure 1) shows rainfall amounts in excess of eight inches have fallen near St. Thomas in the Virgin Islands, and the St. Thomas Airport officially measured 6.61" yesterday--its 5th wettest day in history. St. Thomas has picked up an additional 1.48" today as of 9am AST. Not surprisingly, Flash Flood Warnings are posted for the island. Weather radar out of Puerto Rico shows that a large area of heavy rain will continue to affect the Virgin Islands and eastern Puerto Rico this morning. Martinique radar shows somewhat less activity over the Lesser Antilles.

Satellite loops show STD 17 has a broad, somewhat ill-defined center of circulation, with the heaviest thunderstorms 50 or so miles from the center. This is characteristic of a subtropical storm, which is a hybrid between a tropical storm and an extratropical storm. An upper level low pressure system to the west of STD 17 has pumped cold, dry air aloft into STD 17, keeping it from being fully tropical. As the trough gradually weakens today and Thursday, STD 17 should become fully tropical and intensify into Tropical Storm Otto. Steering currents favor Otto being lifted northwards and then northeastwards out to sea by Friday.


Figure 1. Radar-estimated rainfall from Subtropical Depression Seventeen over Puerto Rico and the Virgin Islands shows that rains in excess of eight inches (white colors) have fallen near St. Thomas.

Elsewhere in the tropics
Most of the models indicate the possibility that a strong tropical disturbance or tropical depression forming in the Southern Caribbean, off the coast of Nicaragua, 5 - 7 days from now.

Monsoon flooding kills 83 in Indonesia, 28 in Vietnam
Heavy monsoon rains triggered flash flooding in a remote section of Indonesia this week that killed at least 83 people. Another 68 people are missing, and 3,000 homeless. In Vietnam, heavy rains of up to 51" (1300 mm) have fallen since Friday, resulting in river flooding that killed at least 28 people. Over 34,000 people are homeless from the floods, which hit five provinces from Nghe An to Thua Thien-Hue, a swath of territory starting some 300 km (180 miles) south of Hanoi and stretching south. Heavy monsoon rains also hit nearby Hainen Island in China, forcing the evacuation of 64,000 people.

Jeff Masters

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Quoting islander101010:
seems to changing to tropical. center of circulation is wrapping up it is unusual looking system on ir


From my understanding of previous NHC reports on old storms, it seems they look for warm core anticyclonic outflow on the storm top to call it tropical. See right now, the ULL is on top of the storm, which indicates that whatever warm core there is is not fully vertical. If that warm core can continue to grow vertically from those nice looking storm clouds, it'll begin "punching out" the ULL, and you'll begin to see the ULL reversing to an ULH (upper-level high), and that upper-level high will be a signature that the warm core sturcture is now fully vertical.

The way you can see that ULH forming is when you start seeing the classic cirrus anticyclonic outflow clouds on the storm top as you would see in a classical tropical storm/hurricane/tropical depression. Another way this can become tropical is that the surface center continues NW and leaves the ULL behind, making it much easier for this thing to develop a warm core ULH.
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Afternoon....Wow....The depression is way off of the forecast points for the moment...That is one huge wobble to say the least.......LOL
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Quoting TropicalMan2010:

lol me too looks very sub-tropical to me


LOL, yep definetly subtropical now. But yesterday at this time on the blog, thre was a debacle using phase diagrams as evidence that this thing was going to be tropical at its declaration. I decided to ignore that phase diagram and look at latest satellite tools analysis on my blog post yesterday to figure out it would be subtropical first, not tropical. I finally am getting the hang of this tropical versus subtropical stuff.
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seems to changing to tropical. center of circulation is wrapping up it is unusual looking system on ir
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Quoting JLPR2:


Ah! Thank you for clearing that up.
As of now the spin is getting dragged NE due to SD 17's circulation, it will be interesting if it actually manages to develop a surface low once it gains enough distance from our storm.

Well, I'm off, college calls. :\


LOL, I should be doing my engineering research work as a grad student right now, but I get distracted sometimes by tropical weather (I also took a meteorology minor in case engineering didn't work out, and use that knowledge in my hobby of tropical weather tracking). I'll leave it at that to keep my identity a secret, LOL.
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Quoting outofdablue:
Floodman, Question Who one this web site deals with personal weather stations? I am interested in setting one up. For some reason I believe you will point me in the right direction. Thanks Kelly


I have a Vantage Pro 2 personal weather station manufactured by Davis Instruments out of California. Very versatile piece of equipment and not overly expensive. I would suggest you visit their web site here to review their offerings.
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204. IKE
Quoting cat5hurricane:
Yep it sure did


I don't see much on the entire run beyond TD17...although it does show a SW Caribbean low at day 16...384 hours. I notice the winds at 200 mb's are just too strong at 180 hours along the northern GOM...through the eastern seaboard....

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202. JLPR2
Quoting NCHurricane2009:


Here's your answer to what that spin just S of Puerto Rico is:
http://www.nhc.noaa.gov/tafb/ATSA_06Z.gif

There is a surface trough attached to the center of our subtropical storm, similar to how there is a cold front attached to an extratropical (non-tropical) storm. Support for the surface trough? The answer is divergence around the rim of the ULL (upper-level low) of the subtropical storm. There tends to be cases of divergence around the ULL's rim as some upper flow swirls into the ULL, some away from the ULL and around other surrounding upper atmospheric features. There has also been such divergence on the south side of the ULL, which supports our surface trough.

That little spin S of Puerto Rico coincides with the surface trough location, perhaps a vortmax on the surface trough.


Ah! Thank you for clearing that up.
As of now the spin is getting dragged NE due to SD 17's circulation, it will be interesting if it actually manages to develop a surface low once it gains enough distance from our storm.

Well, I'm off, college calls. :\
Member Since: September 4, 2007 Posts: 7 Comments: 8733
200. IKE
Quoting cat5hurricane:
12Z GFS (500mb) at 168 hours out.

Not showing the system sitting over the northern coast of Honduras like it was in the previous (6Z) run.



Looks like it's about dropped it on the latest, 12Z run.
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While the GFS backed down on development on this run, I notice something very interesting. The shield is gone! The setup at 180 hours is good for a storm to affect about New Orleans, eastward. Again, this ridge is going to break down and there is a good chance that if anything forms, it would head north as the troughs go by. Hurricane Season still threatens the USA with a good risk for a landfalling Tropical Cyclone.
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ignore feature coming in handy today. howdy WU! hey SE US... let me know if you want some more Minne air :)
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Quoting JLPR2:
Slight spin in the band south of PR.



I don't think it will become anything, but it's pretty to watch. :]


Here's your answer to what that spin just S of Puerto Rico is:
http://www.nhc.noaa.gov/tafb/ATSA_06Z.gif

There is a surface trough attached to the center of our subtropical storm, similar to how there is a cold front attached to an extratropical (non-tropical) storm. Support for the surface trough? The answer is divergence around the rim of the ULL (upper-level low) of the subtropical storm. There tends to be cases of divergence around the ULL's rim as some upper flow swirls into the ULL, some away from the ULL and around other surrounding upper atmospheric features. There has also been such divergence on the south side of the ULL, which supports our surface trough.

That little spin S of Puerto Rico coincides with the surface trough location, perhaps a vortmax on the surface trough.
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195. Skyepony (Mod)
Quoting Floodman:


I'm afraid I can't really help there; anyone have any good info for Kelly on personal weather stations?


Like Chuck said..Aquak9's other half..Rainman ~ he sells them. Priced right & he's great at support too.
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I still say its going west. (kidding, kidding)




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Quoting outofdablue:
Thanks abunch!


No problem - once I find out how much my child support is gonna be, I plan on buying one from them.
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Looks like the 12Z GFS is less aggressive about a SW Caribbean system a week from now than its prior few runs had been.

If anything does start to get going down there, is it likely to be monsoonal a la Nicole? Dr. Masters compared the conditions down there to the way they were pre-Nicole on Hurrican Haven yesterday.

I haven't been sure of what the GFS has been showing in recent runs anyway. It seemed to develop a TS noth of Honduras and then dissipate it at about 200 hours. Was it predicting whatever formed to be sheared apart?
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191. HCW
Quoting PanhandleChuck:


Minus the BP workers, that's an awesome picture


Thanks I can't believe that it was taken with my Iphone 4
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Quoting PanhandleChuck:


I sent her a WUmail with a link to AQUAK9's site
Thanks abunch!
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Quoting HCW:
Can't beat this perfect weather down here at Ft Morgan, AL Now if I could only get the BP worker to move out of my way :)




Minus the BP workers, that's an awesome picture
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187. HCW
Can't beat this perfect weather down here at Ft Morgan, AL Now if I could only get the BP workers to move out of my way :)


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Quoting Floodman:


I'm afraid I can't really help there; anyone have any good info for Kelly on personal weather stations?


I sent her a WUmail with a link to AQUAK9's site
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Quoting cat5hurricane:


Yep, nice satellite imagery. This is one of my favorite looking subtropical cyclones, nice looking storm.
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Quoting JLPR2:
Slight spin in the band south of PR.



I don't think it will become anything, but it's pretty to watch. :]


Vorticity has split to the south from SD17 now too. Yesterday it was joined.
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Quoting outofdablue:
Floodman, Question Who one this web site deals with personal weather stations? I am interested in setting one up. For some reason I believe you will point me in the right direction. Thanks Kelly


I'm afraid I can't really help there; anyone have any good info for Kelly on personal weather stations?
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Quoting cat5hurricane:
Upper Level Divergence


I concur, see the upper divergence on the north side of the system with this sat. loop:

http://www.ssd.noaa.gov/goes/flt/t1/flash-vis.html

By clicking on the HDW-H (high level wind vectors) check box, you can see that the flow on the north side of the ULL is divergent, some of the flow swirls into the ULL, some of it away from the ULL. The divergence is occurring in the area between where the flow goes into the ULL and away from the ULL.
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Quoting outofdablue:
Floodman, Question Who one this web site deals with personal weather stations? I am interested in setting one up. For some reason I believe you will point me in the right direction. Thanks Kelly


AQUAK9
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Quoting PakaSurvivor:
Being new I was wondering if the blog nastiness is normal or just has its moments

LOL - this is why I mostly lurk... there are definitely some individuals who deliberately bait others - when you see the pattern you can put them on ignore and they won't clutter up your reading the blog
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176. JLPR2
Hmm... while Carolina in the North side of the island is reporting winds from the west, in Ponce in the south side of the island is reporting winds from the SE, but the SW and SE sides of the island is still to the west, only the areas closest to the little spin have shifted to the east.

3.0 mph / 4.8 km/h / 1.3 m/s from the SE

That little spin is interesting.
Member Since: September 4, 2007 Posts: 7 Comments: 8733
Yes! I knew it was going subtropical (from NHC first advisory on STD 17):

...SUBTROPICAL DEPRESSION FORMS OVER THE WESTERN ATLANTIC OCEAN...

This is a quote from my blog post yesterday:
"...I am predicting that 97L will become a subtropical cyclone (subtropical depression or subtropical storm) rather than a fully tropical cyclone at its declaration."

If you want to know the distinction between tropical and subtropical, check out my blog post yesterday. In that post, I have a link to another of my posts where I in detail explain the structural difference between tropical, subtropical, and extratropical.
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172. JLPR2
Slight spin in the band south of PR.



I don't think it will become anything, but it's pretty to watch. :]
Member Since: September 4, 2007 Posts: 7 Comments: 8733
Quoting Floodman:


You have vastly underestimated the number of squirrels here, I'm afraid. The fact is, squrrels are drawn by nuts, and, well, we have a large number of them here too
You should know. ;P~

Beautiful day today here at the foot of the Blue Ridge. Crisp air starting to turn the leaves which brings out the Flatlanded Touristers which brings out the Flatfooted Smokey Bears which brings out the speeding tickets. Got to watch my lead foot.
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Floodman, Question Who one this web site deals with personal weather stations? I am interested in setting one up. For some reason I believe you will point me in the right direction. Thanks Kelly
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Skyepony~ I was the one handing out the florida travel brochures to them last year! I think my plan worked.
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Quoting Floodman:


You have vastly underestimated the number of squirrels here, I'm afraid. The fact is, squrrels are drawn by nuts, and, well, we have a large number of them here too
LOL :D
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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.