97L a threat to become a tropical depression on Wednesday

By: Dr. Jeff Masters , 1:31 PM GMT on July 20, 2010

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A tropical wave (Invest 97L) near the east coast of Puerto Rico has become more organized overnight and is a threat to develop into a tropical depression as early as Wednesday. The disturbance has brought heavy rains of 8+ inches to Culebra and Vieques islands over the past day (Figure 1), and all of Puerto Rico and the Virgin Islands are under flash flood watches today. The storm could bring an additional 3 - 6 inches of rain to the islands over the next two days. The upper level low centered a few hundred miles north of the Dominican Republic is no longer bringing high levels of wind shear to 97L; wind shear has fallen to the moderate range, 10 - 20 knots, which may allow 97L to continue to develop today. Satellite images of 97L show a moderate area of disorganized thunderstorms, but no signs of a surface circulation, no low-level spiral banding, and no upper-level outflow. There is a large amount of dry air to the northwest of Puerto Rico that will interfere with development of 97L. Surface observations show only light winds over Puerto Rico, with no signs of a surface circulation. The Hurricane Hunters are on call to investigate 97L this afternoon, if necessary.


Figure 1. Total radar-estimated rainfall from Invest 97L.

Forecast for 97L
The storm is in a fairly straightforward steering current environment, and 97L should progress steadily to the west-northwest through Saturday. The rains from 97L's thunderstorms will bring the threat of flooding to the Dominican Republic today and Wednesday, and to Haiti on Wednesday and Thursday. Heavy rains from 97L will begin moving into eastern Cuba, the Turks and Caicos Islands, and the eastern Bahamas on Wednesday, and South Florida can expect heavy rains to arrive as early as Thursday night. We do have several models developing 97L into a tropical depression or tropical storm. The GFS and HWRF both take 97L to tropical storm status over the Bahamas by Thursday, with the storm then tracking over South Florida on Friday and entering the Gulf of Mexico on Saturday. The NOGAPS is similar, but portrays a weaker system. All of these models foresee a threat to the oil spill region by Saturday night or Sunday, with the storm making a second landfall somewhere between the Florida Panhandle and Louisiana. One factor potentially aiding the storm will be the Madden-Julian oscillation, which currently favors upward motion over the Gulf of Mexico and Caribbean. The Madden-Julian oscillation is a pattern of enhanced rainfall that travels along the Equator from west to east. The pattern has a wet phase with large-scale rising air and enhanced thunderstorm activity, followed by a dry phase with large-scale sinking air and suppressed thunderstorm activity. Each cycle lasts approximately 30 - 60 days. When the Madden-Julian oscillation is in its wet phase over a hurricane-prone region, the chances for tropical storm activity are greatly increased. Also in favor of development are the warm ocean temperatures of 29°C. The SHIPS model predicts shear will remain moderate, 10 - 20 knots, over the next 4 - 5 days, and I believe the primary detriment to development of 97L over the next two days will be the presence of dry, stable air in its path over the Bahamas, thanks to the upper-level low to the north of the Dominican Republic. NHC is giving 97L a 40% chance of developing into a tropical depression by Thursday, which is a reasonable forecast. I think there is a 60% chance 97L will eventually become Tropical Storm Bonnie, sometime in the next five days. Sudden rapid development today or on Wednesday is unlikely, due to the dry air over the Bahamas, and I put the odds of 97L making it to hurricane strength before reaching Florida at 10%. There is a better chance that 97L could attain hurricane strength in the Gulf of Mexico, perhaps 20%. These probabilities will depend heavily upon how long 97L (or Bonnie) spends over land or interacting with land over the next four days, which is very uncertain.

Time to cut the forecast numbers for the coming hurricane season?
Here are the number of Atlantic named storms, hurricanes, and intense hurricanes predicted by the various forecast groups in their late May or early June forecasts:

23 named storms: PSU statistical model
20 named storms: UKMET GloSea dynamical model
18.5 named storms, 11 hurricanes, 5 major hurricanes: NOAA hybrid statistical/dynamical model technique
18 named storms, 10 hurricanes, 5 intense hurricanes: CSU statistical model (Phil Klotzbach/Bill Gray)
17.7 named storms, 9.5 hurricanes, 4.4 intense hurricanes: Tropical Storm Risk (TSR), hybrid statistical/dynamical model technique (Note: TSR increased their numbers to 19.1, 10.4, and 4.8 with their July 6 forecast)
17 named storms, 10 hurricanes: FSU dynamical model
10 named storms, 6 hurricanes, 2 intense hurricanes: climatology

The group forecasting the lowest activity was the Florida State University group led by Dr. Tim LaRow. They use a new dynamical forecast model called COAPS, which is funded by a 5-year, $6.2 million grant from NOAA. This year's June forecast by the COAPS model called for 17 named storms and 10 hurricanes. However, Dr. LaRow emailed me yesterday to say that the COAPS model is now calling for reduced activity. Using the state of the atmosphere and ocean as of July 15, a new run of the COAPS model was performed over the weekend. The new forecast is now calling for two fewer hurricanes--a total of 15 named storms and 8 hurricanes (including Alex.) The COAPS model generated an "ensemble" of five different forecasts, done by varying the initial sea surface temperatures by a few percent at the beginning of the model run. These five forecasts came up with a range of 12 - 16 named storms (including Alex), and 7 - 10 hurricanes. It will be interesting to see when CSU issues its August 4 forecast if they also cut their numbers. With only one named storm (Alex) thus far this year, it's getting pretty hard to have a season with 19 or 20 named storms. Only four hurricane seasons since 1851 have had as many as nineteen named storms. These four seasons--1887, 1933, 1995, and 2005--all had at least three named storms by July 20.

"Hurricane Haven" airing again this afternoon
Tune into another airing of my live Internet radio show, "Hurricane Haven", at 4pm EDT today. Listeners will be able to call in and ask questions. The call in number is 415-983-2634, or you can post a question in the comments area on my blog during the show. You can also email the questions to me today before the show: jmasters@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line. Some topics I'll cover today on the show:

1) Invest 97
2) A look ahead at the coming two weeks

Today's show will be about 45 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast.

Jeff Masters

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oh hell no!!! should I expect tropical storm conditions Friday night in South Florida or just a rain event? I need to make sure flight plans will not be affected :(
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I dont like the gfs
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1286. gator23
Quoting StormW:


For FL.

right that is what Jeffs was talking about, Florida. the GFDL and HWRF models have shifted north in his estimation.
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July Development probability :



August Development probability :



interesting..
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Quoting MiamiHurricanes09:
An area of low pressure is obviously there.


He's incorrect. You can have a surface low without having a closed circulation.
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Quoting StormW:


Only in short term.



hmmm......right?
Member Since: September 1, 2007 Posts: 0 Comments: 1793
1279. Drakoen
You can see the circulation on radar north of the eastern tip of Hispaniola
Member Since: October 28, 2006 Posts: 57 Comments: 29714
1278. gator23
Quoting StormW:


Only in short term.

3 days until landfall is what the GFS is showing is that not considered short term?(sarcasm flag down) I legitmately want to know this.
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wow this blog has officially gone NUTS lol!! hate to see it when it does become Bonnie...
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1276. hydrus
Quoting FLdewey:
Reed's computer desk obviously leans.
lol
Member Since: September 27, 2007 Posts: 1 Comments: 19521
looks more and more likely south florida will have rough weather this weekend regardless
Member Since: July 14, 2009 Posts: 0 Comments: 2990
Quoting CyclonicVoyage:


They said it SUGGESTS a surface center is becoming better defined. Until it's closed, it's not a surface low, it is a center of circulation.
An area of low pressure is obviously there.
Member Since: September 2, 2009 Posts: 130 Comments: 21032
NHC 60%

Link
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Look, am I the only one here that thinks Miriam Stockly has a great voice?
Member Since: September 1, 2007 Posts: 0 Comments: 1793
Last update of his own blog:
Posted by: Weather456, 5:08 AM EST on July 19, 2010
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1268. gator23
Quoting MiamiHurricanes09:
Well it does have an LLC.

it is not a closed LLC, it is not there yet. We are splitting hairs. Florida from Jax to the Keys needs to watch out. If the storm strengthens then they could just as easily shift north.
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1266. leo305
Quoting CyclonicVoyage:


They said it SUGGESTS a surface center is becoming better defined. Until it's closed, it's not a surface low, it is a center of circulation.


actually it is a surface low, just not completely closed off.
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Quoting StormW:


LMAO Flood!


LOL...it's true, huh?
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UNISYS View:


Puerto Rico NWS Radar:

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Quoting MiamiHurricanes09:
Isn't a circulation that is in the lower levels a LLC? In the TWO they said that it had an area of low pressure (evident on satellite and surface observations).


They said it SUGGESTS a surface center is becoming better defined. Until it's closed, it's not a surface low, it is a center of circulation.
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1260. leo305
Quoting CaribbeanIslandStorm:

What location?


20N 68.2W

based on visible satellite.
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1259. xcool
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Quoting gator23:

well, for me the LLC means a circulation down to the surface that is vigorous, and formed. The LLC is forming, but at this stage new LLC's can form anywhere.
Well it does have an LLC.
Member Since: September 2, 2009 Posts: 130 Comments: 21032
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Quoting CaribbeanIslandStorm:

What location?
The area of low pressure is located north of the eastern tip of the Dominican Republic. Below are the exact coordinates.

AL, 97, 2010072018, , BEST, 0, 195N, 682W, 30, 1012, DB,
Member Since: September 2, 2009 Posts: 130 Comments: 21032
Quoting jasoniscoolman2010x:
WOW THAT WAVE COMING OFF OF AFRICA IS BIG WITH SOME SPIN TO IT.
Link Yes it's a large one...and appears to have at least a partially closed low level circulation.
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1253. gator23
Quoting MiamiHurricanes09:
Isn't a circulation that is in the lower levels a LLC? In the TWO they said that it had an area of low pressure (evident on satellite and surface observations).

well, for me the LLC means a circulation down to the surface that is vigorous, and formed. The LLC is forming, but at this stage new LLC's can form anywhere.
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Quoting patrikdude2:


Big wave from Africa coming!


Way scary stuff.
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Quoting StormW:


I gotta wait for the updated shear forecast map. As of the 12Z run, upper air pattern didn't support a major.


ok...thanks! Keep me in mind if your "feelings" change! :)
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No no no, you all don't understand, I'm not talking about the dynamic models..



Notice a westward, left hook at the end of the BAMM runs..

Now check these out..



Better agreement, some went north, some went south and came closer together.. That's what I'm trying to explain.. But nevermind.
Member Since: July 1, 2008 Posts: 13 Comments: 7334
Quoting StormW:
Now, on model guidance...do I believe the actual tracking? Not at this time. Best things for systems like this is satellite imagery and forecast steering layers maps.


I've nothing to say, just think that bears repeating
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1247. Drakoen
Quoting moonlightcowboy:
The models are guessing, having no definitive LLC, it's all a guess. This board places way too much emphasis on modeling, especially when there's little to "model."

Let's get an LLC, a bit stouter and stacked system, then the models will likely have a more significant grip on the system. Right now, they're more likened to one wearing a blindfold, throwing darts at a target. When they can see, they'll be much more accurate.


There is a low pressure center north of the eastern tip of Hispaniola that is discernable on satellite imagery. According to the cimss vorticity charts this is stacked fairly up to 700mb.

Enough vorticity for a computer to model.
Member Since: October 28, 2006 Posts: 57 Comments: 29714
Quoting leo305:
we do have a low level center, it just isn't closed yet.. once it's closed, we have a TD.

What location?
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StormW....what do you think of SE LA/SW MS getting a major cane out of this? Any reality in that???


I can answer that. YES...it's possible. It's theoretically possible that a cat 5 will be bearing down on the area in less than a week.

which, imho...will happen
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Quoting StormW:
Now, on model guidance...do I believe the actual tracking? Not at this time. Best things for systems like this is satellite imagery and forecast steering layers maps.
Steering from PSU shows about the same thing as the models in terms of track.
Member Since: September 2, 2009 Posts: 130 Comments: 21032
For it being just an invest area, I'm surprised at how good the models are agreeing... well actually they agreed better on the 12z run than they did for the 18z..
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Quoting StormW:


No, I haven't...in fact, haven't seen Levi either.

They've both been extremely quiet lately, I love to hear they're input on matters as well yours.
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Quoting mikatnight:


There's a lot of shift being tossed around on the blog all the sudden. I think everyone should just take a deep breath and get their shift together.


And some will be getting their shift out of town...
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1239. leo305
we do have a low level center, it just isn't closed yet.. once it's closed, we have a TD.
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Quoting gator23:

oh sorry i forgot my sarcasm flag, Sarcasm flag up.


I had no idea it was ever down...
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About JeffMasters

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