Tropical Depression Seven forms

By: Dr. Jeff Masters , 2:25 PM GMT on August 14, 2011

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The latest in our unusual number of weak tropical cyclones this season, Tropical Depression Seven, has formed to the southeast of Bermuda. Unless you live in Bermuda, TD 7 is not going to be a concern. Radar out of Bermuda shows an area of rain on the northern side of TD 7 beginning to approach the island, and rain from the storm will likely affect the island tonight and on Monday. TD 7 is not well-organized, and has only limited heavy thunderstorms, as seen on visible satellite images. While wind shear is a low 5 - 10 knots, dry air surrounds TD 7, and is keeping the storm from intensifying. None of the computer models foresee that TD 7 will ever become more than a weak tropical storm.


Figure 1. Morning satellite image of TD 7.

92L
TD 7 isn't the only system Bermuda needs to watch, Invest 92L is a day behind it, and will follow a path very similar to TD 7's. The disturbance will pass close to Bermuda on Tuesday, bringing the island a second round of tropical rains. However, Invest 92L is very disorganized, as seen on recent visible satellite loops. Dry air and close proximity to TD 7 will likely keep 92L from showing significant development over the next two days, with NHC giving the system just a 30% chance of developing into a tropical depression by Tuesday morning.

Elsewhere in the tropics
The disturbance midway between the Lesser Antilles Islands and the coast of Africa we've been tracking over the past few days, Invest 93L, has fallen apart and is no longer a threat to develop. This system will need to be watched once it enters the Caribbean later this week, though. None of the reliable models for predicting tropical cyclone formation predict development of this system or any new disturbances over the coming week.

Jeff Masters

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Quoting P451:



You've had a real good handle on this system from the start.

A lone voice of reason swamped by days of repeated calls for a major hurricane to develop and decimate the Caribbean.



Thanks, lol. 93L had "teaser" written all over it from the beginning.
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SUBJECTIVE LIST OF MODEL PERFORMANCE CHARACTERISTICS

The NCEP model suite is upgraded numerous times annually. Since each "model" is actually a system of integrated components, even slight “tweaks” to any of the components can drastically effect the model's performance characteristics. For example, the Global Forecast System (GFS) consists of the initialization scheme (Global Data Assimilation Scheme - GDAS), the Global Model itself, and the post processed grids that are made available for use in grid and grib format. Even a slight modification to any one of these components can drastically effect the perceived performance of the model. As a result it is not only difficult to isolate consistent model performance characteristics (loosely referred to as “bias”) across the model upgrades, but also the source of the bias. subjective list of model performance characteristics (biases) have been obtained via forecasters
in order for EMC to gain a more complete picture of model performance, all users of NCEP model output should provide their subjective observations of model performance by submitting their subjective observations of bias.
This information will be conveyed to HPC and EMC and potentially added to this web page.

Link
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Quoting CaicosRetiredSailor:
Another piece of the 2011 puzzle:
Surface currents

Quote from AntiguaIsland,blogspot:

We had months of unusual south currents and many of us who were fishing in May and June complained about these currents. It seems as though they hit the Sargasso Sea at a strange angle possibly pushing some of the weed away from what is normally a current free area within the north Atlantic gyre. Its as if - in a swirl - masses of sargassum broke off and probably went north and east into the currents which now have brought the weeds back across from Africa into the Caribbean. People from Tobago to Hispaniola are complaining about masses of weeds. This photo below taken by a friend shows what is normally a nice little windward bay on the Eastern side of Antigua. As you can see, the dock is now surrounded by sargassum.
This is weird. The sea and shore in East End, Grand Cayman is covered with this. Never saw it like that before.
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1871. emcf30
I see 93L was re-activated as many were saying was a possibility on here yesterday. Dry air West of 93L will probably keep it from developing until it reaches the West Caribbean but we are going to have to watch this closely.

Also, our next AOI has come off the cost of Africa. Going to be a interesting couple of weeks
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Quoting spathy:


Thanks Kman

I thought that seemed odd.


We see this all the time. The models are assuming many things to give the results you see but without a closed low to work with early forecasts for intensity tend to be more wrong than right. Doesn't mean it cannot happen but typically it does not play out that way early on.

Once you have a TD that changes.
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Another piece of the 2011 puzzle:
Surface currents

Quote from AntiguaIsland,blogspot:

We had months of unusual south currents and many of us who were fishing in May and June complained about these currents. It seems as though they hit the Sargasso Sea at a strange angle possibly pushing some of the weed away from what is normally a current free area within the north Atlantic gyre. Its as if - in a swirl - masses of sargassum broke off and probably went north and east into the currents which now have brought the weeds back across from Africa into the Caribbean. People from Tobago to Hispaniola are complaining about masses of weeds. This photo below taken by a friend shows what is normally a nice little windward bay on the Eastern side of Antigua. As you can see, the dock is now surrounded by sargassum.


http://antiguaisland.blogspot.com/2011/08/sargass um-come-ashore-in-unprecedented.html

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Quoting kmanislander:


Intensity forecasts for a system that is not even a TD yet are unreliable.


And that might even be an understatement.
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Member Since: June 2, 2010 Posts: 0 Comments: 1404
Quoting stormpetrol:


Wind shift from the approaching wave. No well defined surface low as yet though, just a broad area of low pressure.
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Quoting spathy:
The model forecast for 93L is interesting.
Does anyone think this is likely?




Intensity forecasts for a system that is not even a TD yet are unreliable.
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1861. SLU
Quoting pottery:
DAM!
It looks like this Hot Dry weather is going to stay around for a while....


lol.

Intense thunderstorms and heavy rains sweeping across St. Lucia after a week of March-like dry weather. You should get some this afternoon as a result of daytime heating with the increased moisture around now.
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Quoting KennyNebraska:
The current model tracks for 93L are disconcerting. The GoM is full of very hot water.


Yes it is.... I can personally attest to the hot water. I was in clear water (tampa fl.) last week and the beach was so hot that I jumped into the water and it was very un-refreshing. I told my wife that I was still sweating in the water.. LOL
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93L might end up like Don or Emily if dry air has its say.
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Link
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1855. ncstorm
look for another frontal boundary coming off the east coast

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Quoting pottery:
DAM!
It looks like this Hot Dry weather is going to stay around for a while....


Afraid so for you. 93L passing to your North as we discussed a few days ago.
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The current model tracks for 93L are disconcerting. The GoM is full of very hot water.
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1851. pottery
DAM!
It looks like this Hot Dry weather is going to stay around for a while....
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I wish we had HH data for Gert...:{
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1849. ncstorm
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Quoting hurricane23:


Just for fun 06z GFS developes the wave currently rolling of africa into a pretty formidable cane.

is that the wave coming off africa right now?
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Convection increasing closer to the center.
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Quoting earthlydragonfly:


Thanks
most welcome
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1844. HCW
Latest NHC model runs for 93L

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Good Morning

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Quoting HurricaneHunterJoe:
possible diurnal max?


Diurnal max is gone for today and wont return until around 5 am tomorrow morning. Diurnal min will be just before sunset today.
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1841. rod2635
For those needing a break from 93's status in the Tropial ER, invest 98, whose center lost its convection yesterday, has regained it. Still heading Hawaii way. Interesting only in that they don't often get storms...small land mass target, low storm survival rates requiring long westerly tracks to stay amenable water temps.
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Quoting HurricaneHunterJoe:


Doesn't look all that far off being a hurricane, and it has probably another 24 hours of strengthening. We might just scrape 7-1-0.
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Quoting Tazmanian:




for the two plzs look at the past commets like 1830


or the 10 others
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Quoting BobinTampa:
just checking in, could someone post the TWO and Bermuda radar?

:/




for the two plzs look at the past commets like 1830
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1837. SLU
Quoting asdip:


Marigot Bay. Heavy rain too.
Quoting asdip:


Marigot Bay. Heavy rain too.


Hmmmm ... a lot more is on the way.
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lol
Member Since: May 27, 2009 Posts: 0 Comments: 4438
just checking in, could someone post the TWO and Bermuda radar?

:/
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Quoting HurricaneHunterJoe:
Link


Thanks
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Quoting GeorgiaWx65:
000
ABNT20 KNHC 151157
TWOAT

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT MON AUG 15 2011

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM GERT...LOCATED ABOUT 100 MILES SOUTHEAST OF BERMUDA.

A TROPICAL WAVE LOCATED ABOUT 325 MILES EAST OF THE LESSER ANTILLES
IS PRODUCING A LARGE AREA OF CLOUDINESS AND THUNDERSTORMS.
DEVELOPMENT OF THIS DISTURBANCE...IF ANY...SHOULD BE SLOW TO OCCUR
DURING THE NEXT COUPLE OF DAYS. HOWEVER...THIS DISTURBANCE WILL
PRODUCE BRIEF PERIODS OF LOCALLY HEAVY RAINFALL AND STRONG GUSTY
WINDS OVER PORTIONS OF THE CENTRAL AND NORTHERN LESSER ANTILLES
TODAY THROUGH TUESDAY. THIS SYSTEM HAS A LOW CHANCE...10 PERCENT...
OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES
WESTWARD AT 15 TO 20 MPH.

SHOWER AND THUNDERSTORM ACTIVITY HAS CONTINUED TO DIMINISH IN
ASSOCIATION WITH A BROAD AREA OF LOW PRESSURE LOCATED ABOUT 650
MILES NORTH OF THE NORTHERN LEEWARD ISLANDS. ENVIRONMENTAL
CONDITIONS ARE BECOMING LESS CONDUCIVE FOR DEVELOPMENT OF
THIS SYSTEM OVER THE NEXT COUPLE OF DAYS DUE TO PROXIMITY TO
TROPICAL STORM GERT. THIS SYSTEM HAS A LOW CHANCE...NEAR 0
PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS
AS IT MOVES TOWARD THE NORTH-NORTHWEST OR NORTH AT 15 TO 20 MPH.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER STEWART



pls see post 1815
Member Since: May 21, 2006 Posts: 5091 Comments: 115454
Good morning guys! I see 93L is born again, and check out Gerty on radar...perhaps our hurricane drought will be over today.

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Quoting stormwatcherCI:

Yep, not ideal for development.It would do much better with 10 to 15. Its current speed will tend to hinder development but not fatal. I have seen TDs form at 20 to 25 but under ideal conditions.
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1827. Patrap
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93L has about 24 hours to get to the Windwards. Convection is nice, but probably little underneath yet. Probably more than 10%, but it doesn't have a great deal of time to do something.

Is it an Emily (forms in the nick of time) or a Don (prefers the Western Caribbean) or most tropical waves that do nothing?

TCHP is likely to rise with this one (Tropical Cyclone Hyperbole Potential).
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1825. asdip
Quoting SLU:


Where are you located?


Marigot Bay. Heavy rain too.
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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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