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 gator23:

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


I had no idea it was ever down...
Member Since: August 2, 2006 Posts: 10 Comments: 9922
Quoting CybrTeddy:
Pressures beginning to drop in Puerto Rico.
must be a sign of a T.D. forming....?
Member Since: Posts: Comments:
Quoting CyclonicVoyage:


We have a potential LLC, still not closed yet.



ALTHOUGH THE SYSTEM DOES NOT YET HAVE A CLOSED CIRCULATION...
SATELLITE IMAGERY SUGGESTS THAT A SURFACE LOW PRESSURE AREA IS
BECOMING BETTER DEFINED JUST NORTH OF THE EASTERN TIP OF
HISPANIOLA.
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).
Member Since: September 2, 2009 Posts: 130 Comments: 21178
Quoting StormW:


'xcuse me...hi! Which way are the tracks pointing more from 12Z to 18Z?

12Z


18Z



StormW....what do you think of SE LA/SW MS getting a major cane out of this? Any reality in that???
Member Since: September 25, 2007 Posts: 0 Comments: 207
Quoting sporteguy03:

He is around I know he said he only comes on occasionally to the blog, although it would be nice to hear his input today.


It would be nice, I really like what 456 and StormW has to say, there just about on the same page when it comes to this stuff. We miss ya 456.

Sheri
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1231. gator23
Quoting MiamiHurricanes09:
AL, 97, 2010072018, , BEST, 0, 195N, 682W, 30, 1012, DB,

hmmm...
Member Since: August 26, 2008 Posts: 0 Comments: 2165


warm waters ahead of 97L
Member Since: Posts: Comments:
Pressures beginning to drop in Puerto Rico.
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Does anyone think that the big african wave could 'sacrifice' itself to moisten up the atmosphere and get rid of some of the SAL?

Noticed that models have shifted left, hope it doesn't affect the oil spill too much!
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Quoting sailingallover:

ditto and it looks like it's breaking free of PR finally..
see what the wind and pressure do at arecibo
If it turns westerly and drops


Yep. Should see better definition, that lower circulation, and pretty much all the ingredients comming together.

Member Since: Posts: Comments:
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.
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Quoting gator23:

where is the LLC.
AL, 97, 2010072018, , BEST, 0, 195N, 682W, 30, 1012, DB,
Member Since: September 2, 2009 Posts: 130 Comments: 21178
Quoting MiamiHurricanes09:
We have a LLC and 1 correct initialization point.


We have a potential LLC, still not closed yet.



ALTHOUGH THE SYSTEM DOES NOT YET HAVE A CLOSED CIRCULATION...
SATELLITE IMAGERY SUGGESTS THAT A SURFACE LOW PRESSURE AREA IS
BECOMING BETTER DEFINED JUST NORTH OF THE EASTERN TIP OF
HISPANIOLA.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting StormW:


shift caster.


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.
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MS/AL/Panahandle Hurricane in the cards for early next week... which could actually possibly help push a lot of the oil back out to sea? possibly?
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Quoting FLdewey:


one hop this time
one hop this time
reverse,reverse
slide to the left
slide to the right
reverse,reverse

This is the perfect 97L track forecast. Just wait.
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1217. gator23
Quoting MiamiHurricanes09:
We have a LLC and 1 correct initialization point.

where is the LLC.
Member Since: August 26, 2008 Posts: 0 Comments: 2165


Big wave from Africa coming!
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1213. gator23
Quoting StormW:


'xcuse me...hi! Which way are the tracks pointing more from 12Z to 18Z?

12Z


18Z


oh sorry i forgot my sarcasm flag, Sarcasm flag up.
Member Since: August 26, 2008 Posts: 0 Comments: 2165
Quoting StormW:


?????????


StormW~ Great call today. You the man.

Sheri
Member Since: Posts: Comments:
if you look at the map of the models straight on with both eyes open, they shift left. but if you close your right eye, they shift right.
Member Since: July 30, 2007 Posts: 6 Comments: 1448
Quoting gator23:

it kinda doesnt matter until we have a LLC.
We have a LLC and 1 correct initialization point.
Member Since: September 2, 2009 Posts: 130 Comments: 21178
Quoting Drakoen:


19.5N 68.2W

ditto and it looks like it's breaking free of PR finally..
see what the wind and pressure do at arecibo
If it turns westerly and drops
Member Since: Posts: Comments:
Seems to me people do not know their Directions ( west,north,south,east ) The disturbed weather definitely took a SW Shift.
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1206. gator23
Quoting MiamiHurricanes09:
Well you're calling it incorrectly. You could only call the shift seen on the 18z runs 2 things, and that is a southward shift or a shift towards the left. In no way did the models move towards the north.

it kinda doesnt matter until we have a LLC.
Member Since: August 26, 2008 Posts: 0 Comments: 2165
1204. est1986
come to louisiana please! :D
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The 97L reminds me Jeanne (2004) ... Haiti could be seriously affected in a few days
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Quoting StormW:


shift caster.


most could take out the F! LOL
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Quoting StormW:


?????????


Well what I meant to say was (sigh, rubs his forehead) while some shifted left, others like the BAM model shifted right, well north actually.. Like look at the 12Z runs of the BAMM runs, notice the hook westward.. Then look at the new runs and you'll see a shift to the right in the end, no hook to the west, a general west-northwestward direction.. That's what I meant to say, in conclusion, the models have come into a better alignment.
Member Since: July 1, 2008 Posts: 13 Comments: 7365
Member Since: September 2, 2009 Posts: 130 Comments: 21178
Quoting patrikdude2:


Dark purple looks scary.


So many things left to happen. I kinda thought a track in between the light purple and light blue.

I heard the term "cone of uncertainty" one time being used to determine the landfall of a hurricane.
Member Since: Posts: Comments:
1197. unf97
Quoting StormW:


I know that...only thing I was doing was calling for a shift left at 18Z


Yes you did StormW. I remembered that post a couple of hours ago, and you nailed that left shift for the next run at 18Z. That's why you are so respected sir!!
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Quoting StormW:


shift caster.

Mr. Storm, have you heard from 456 lately ?
Member Since: Posts: Comments:
Quoting MiamiHurricanes09:
Well you're calling it incorrectly. You could only call the shift seen on the 18z runs 2 things, and that is a southward shift or a shift towards the left. In no way did the models move towards the north.


agreed not sure what reed is seeing
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the question is how far left will it shift
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Quoting reedzone:


Northward shift, thats what I call it, definitely not hooking towards the west as the 12Z.. More of a WNW track.
Well you're calling it incorrectly. You could only call the shift seen on the 18z runs 2 things, and that is a southward shift or a shift towards the left. In no way did the models move towards the north.
Member Since: September 2, 2009 Posts: 130 Comments: 21178
Quoting AlexEmmett:

the water its near is hotter then meghan fox


i dunno man. lol
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See storm2 thats what i dont like. Dont want to see that strenthen and skirt the keys and then decide she wants to see santa claus via the pinellas county highway.
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Quoting sailingallover:

When I talked to my friends in Culebra a couple hours ago they were asking why I was not there just in case...the harbor there is the best place to be in a boat in a storm.
I would have had to leave Saturday..but didn't for the last 36 hours it would have been crazy to try to go over there even though it's only 18 miles. Did anybody expect this wave to slow down and the convection to sit over us this long on Saturday?
So maybe a little early planning is best although I don't think anything happened this time..but it would have been very difficult for me to do anything yesterday or today..

Did you see the huge wave that just came off of africa? in the latest pass, there seems to be a circulation, and high winds.
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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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