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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Quoting Drakoen:


Conservatively yes
Conservatively? Oh man, how about without conservativeness, lol?
Member Since: September 2, 2009 Posts: 130 Comments: 21032
Good morning all!
Rainy morning in Puerto Rico... third in a row.
I just woke up and see 97 has been working hard all night. lol
One question, is there a new center over Vieques? The radar loop out of San Juan shows circulation over the Anegada Passage... I know yesterday it was clearly north of Puerto Rico, but has a new low formed to the east?
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Quoting Seflhurricane:
Drak based on the models we may have a strong TS appoaching South Floirda ??? and yes i agree with you 97L is getting much better organized


Conservatively yes
Member Since: October 28, 2006 Posts: 57 Comments: 29714
Reminds me of Erin in 1995.

http://en.wikipedia.org/wiki/Hurricane_Erin_(1995)
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Quoting FLdewey:
Ants in ma sugar :-|
Eat them.....ther yummi..:)
Member Since: September 27, 2007 Posts: 1 Comments: 19504
83. IKE
Quoting StormSurgeon:


I know, just saying that I'm glad it's interacting with land and hopefully inhibiting development. Need all the help we can get....right?


Yup. Biggest thing now is the rain.
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12z sounding from San Juan suggests a circulation in the mid levels (600-700mb).

Member Since: September 2, 2009 Posts: 130 Comments: 21032


Not much doubt from models where they think the future "Bonnie" is going.




Dang look how the HWRF just keeps climbing.
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Hi Storm! I'm going to read your blog because if I keep reading this blog I would think that there was going to be a hurricane here in a couple of day....lol...
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Quoting IKE:


Looking at the 252NM SJ,PR radar, it looks like it's gotten slightly better organized and is moving WNW.


I know, just saying that I'm glad it's interacting with land and hopefully inhibiting development. Need all the help we can get....right?
Member Since: September 1, 2007 Posts: 0 Comments: 1793
Hey tampa, thanks for that email today about 97L. I forgot I signed up for that on your site.
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Wind shear has increased over 97L and also in it's path (30-40 knots). I have a hard time believing that conditions will become favorable so quick.
Member Since: July 1, 2008 Posts: 13 Comments: 7334
Quoting StormW:
INVEST 97L AND AREAS OF INTEREST SYNOPSIS ISSUED 9:40 A.M. JULY 20, 2010


Thanks Storm!!! Am in Key west so am watching.
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Quoting Drakoen:


Yea
Drak based on the models we may have a strong TS appoaching South Floirda ??? and yes i agree with you 97L is getting much better organized
Member Since: July 14, 2009 Posts: 0 Comments: 2990
All this talk about 97L, what's going on with the Tropical Wave?
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Quoting reedzone:


Haha thank God for that wind shear or else with those water temps and TCHP, we would be in BIG trouble.


THE TCHP is already there......

Quoting Drakoen:
Looks like the models have come into a tight cluster taking the system over South Florida and into the western GOM where it may feel the effects of a trough and start to move more towards the north.


Very simple Steering in place with this it appears! We better hope she does not organize faster than models are predicting, which is possible as the TUTT is about go POOOF also.
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Quoting mara0921:
Good morning everyone. I live in Broward County, FL. Needless to say the last thing I want is storm making a surprise apprearance this weekend. I decided to look at todays developments and was a little shocked by whats happpening. The computer models and intensity forecast at first glance are worrisone. Could some please fill me in on this wave/depression and if it has a chance to make it to hurricane strength ? thanks I'll check back when I get to work.


I feel your concern, just keep watching, like the rest of us, but don't rush to Lowes just yet.......
Member Since: September 1, 2007 Posts: 0 Comments: 1793
This scenario will certainly push some oil into the loop current and up the gulf stream
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Member Since: October 28, 2006 Posts: 57 Comments: 29714
63. 7544
getting more stronger now darker reds showing up is the pres starting to fall again ?
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62. IKE
Quoting StormSurgeon:


PR is knocking the wind out of it......


Looking at the 252NM SJ,PR radar, it looks like it's gotten slightly better organized and is moving WNW.
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Quoting btwntx08:

meant eastern gom


Yea
Member Since: October 28, 2006 Posts: 57 Comments: 29714
Good morning everyone. I live in Broward County, FL. Needless to say the last thing I want is storm making a surprise apprearance this weekend. I decided to look at todays developments and was a little shocked by whats happpening. The computer models and intensity forecast at first glance are worrisone. Could some please fill me in on this wave/depression and if it has a chance to make it to hurricane strength ? thanks I'll check back when I get to work.
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Quoting IKE:
On the move now?




PR is knocking the wind out of it......
Member Since: September 1, 2007 Posts: 0 Comments: 1793
57. IKE
NHC track has it going just north of Haiti/DR.
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thanks Dr.Jeff, your information is very important for me, from CUBA, Rosy
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I'm hoping for rain here in South Florida...it just doesn't seem like we have had very much...
I'm sure that it won't develope into much of anything until it gets in the gom......
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...SPECIAL FEATURE...

AN AREA OF DISTURBED WEATHER IS OVER THE LEEWARD ISLANDS...
PUERTO RICO...AND HISPANIOLA ASSOCIATED WITH A TROPICAL WAVE
ALONG 71W...AND UPPER LEVEL DIFFLUENT FLOW FROM AN UPPER LEVEL
LOW CENTERED N OF HISPANIOLA NEAR 26N68W MOVING SW. RECENT
UPPER-AIR DATA INDICATE THE SYSTEM IS BECOMING BETTER ORGANIZED
IN THE MIDDLE AND UPPER LEVELS OF THE ATMOSPHERE.
THERE IS A
MEDIUM CHANCE OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS AS THE DISTURBANCE MOVES WEST-NORTHWEST.
REGARDLESS OF DEVELOPMENT... LOCALLY HEAVY RAINFALL AND GUSTY
WINDS COULD AFFECT THE NORTHERN LEEWARD ISLANDS...THE VIRGIN
ISLANDS...PUERTO RICO...THE DOMINICAN REPUBLIC...HAITI...EASTERN
CUBA...THE TURKS AND CAICOS ISLANDS...AND THE SOUTHEASTERN
BAHAMAS DURING THE NEXT COUPLE OF DAYS.

Member Since: October 28, 2006 Posts: 57 Comments: 29714
53. IKE
Quoting 34chip:
So the Florida Keys are in the line of fire.


I would say yes.
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ridge over the SE is the driver, intense ridge means farther west and south, weaker means farther North
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I am sure Baha won't be too excited about 97L's potential.
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So the Florida Keys are in the line of fire.
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The next 24hrs is very Critical as the the Strenght 97L will be when it gets to South Florida. The stronger it becomes the more Northward the future Bonnie will go.
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Quoting Drakoen:
Oh and 97L is establishing upper level outflow. Look at the satellite images and notice the clouds/convection north of Puerto Rico fanning out to the northeast.

Excellent satellite view of 97L
Possible anticyclone?
Member Since: September 2, 2009 Posts: 130 Comments: 21032
46. 7544
this should get the local news at 11am see what they say
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what is the time frame for 97L or Bonnie to approach South florida and the SE bahamas vicinity
Member Since: July 14, 2009 Posts: 0 Comments: 2990
Oh and 97L is establishing upper level outflow. Look at the satellite images and notice the clouds/convection north of Puerto Rico fanning out to the northeast.

Excellent satellite view of 97L
Member Since: October 28, 2006 Posts: 57 Comments: 29714
43. IKE
On the move now?


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Why, the one weekend that I actually plan on vacation does there have to be a "threat" of a storm. Hope it stays away from here, and isn't more than a little rain for anyone else!
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Quoting reedzone:


Haha thank God for that wind shear or else with those water temps and TCHP, we would be in BIG trouble.


4 days is a long time for a storm to get it's act together
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Well thanks for the update Dr Masters.

I guess my post I put in prev blog around 9:30am has been answered. :o)


We may see some much needed rain come Thur/Fri here in the SE Fla area....
hope that is all we see from this system.



So I will be checking in and out today and tomorrow to get your thoughts and updates.

You all have a great day and enjoy tracking the development of this system.

Gamma
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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.