98L organizing; September temperatures in the U.S. return to normal
A tropical wave midway between Africa and the Lesser Antilles (Invest 98L) continues to look well-organized on satellite imagery, with a modest amount of heavy thunderstorm activity and excellent spin. An ASCAT pass from 7:47 pm EDT last night showed that 98L had a moderately well-defined surface circulation. Wind shear as diagnosed by the SHIPS model is light, less than 10 knots, and is predicted to stay light to moderate through Friday. Ocean temperatures are 28 - 28.5°C, well above the threshold typically needed for a tropical storm to spin up. Water vapor satellite images show 98L is embedded in a moist environment, but there is dry air to the system's northwest. However, given the light wind shear, this dry air may not pose a hindrance to development at this time. An analysis of upper level winds from the University of Wisconsin CIMMS group shows a pattern favorable for development, with an outflow channel open to both the north and south available to ventilate the storm and allow 98L to efficiently lift plenty of moisture to high levels.
Figure 1. Morning satellite image of 98L.
The models are not very aggressive about developing 98L into a tropical storm, but most of them do show some development. NHC gave the disturbance a 70% chance of developing into a tropical depression by Thursday in their 8 am Tropical Weather Outlook. 98L's westward motion of 5 - 10 mph should bring the storm into the Lesser Antilles Islands by Saturday, though the models are not in strong agreement about the forward speed of the storm. The GFDL model brings 98L into the islands on Friday, while the NOGAPS model keeps the storm east of the islands through Tuesday. If 98L takes a more west-northwesterly path through northern Lesser Antilles, which has been the preferred track for tropical systems this year, the disturbance should encounter high wind shear in excess of 20 knots due to strong upper-level winds out of the west. This shear should make it difficult for 98L to intensify as it moves though the islands. However, if 98L takes a more southerly path across Barbados, as predicted by the GFDL model, the storm will miss seeing the high shear area that lies over the northern islands, and the storm would have more opportunity to strengthen. The most likely scenario I see at this point is for 98L to be a weak tropical storm on Saturday as it moves through the Lesser Antilles--but there is more than the usual amount of uncertainty in both the track and intensity forecast.
September temperatures return to normal over the U.S.
The summer of 2011 was the second hottest in U.S. history, but September of 2011 is so far shaping up to be an average one for temperature. A series of cold fronts and cold-cored low pressure systems have moved southwards out of Canada this month, bringing typical amounts of cool air to the country. If you want to select dates for the start and end of the U.S. heat wave of 2011, the dates to pick would be May 20 - September 4. During the period May 20 - September 4, 2011, the number of daily record high temperatures at the 515 major airports in the U.S. exceeded the number of daily low temperature records every day but one. That's an astonishing 107 out of 108 days! Only July 15 had more record daily lows than highs during that 108-day period. I doubt one could find a similar stretch of days anytime in U.S. weather history where such a lopsided ratio of high temperature to low temperature records existed. For the 3-month summer period of June, July, and August, 2703 daily high temperature records were set, compared to 300 daily low temperature records--a ratio of 9-to-1. Not surprisingly, the summer of 2011 wound up as the hottest summer in 75 years in the U.S., and was only 0.1°F cooler than the all-time record hottest summer, during the Dust Bowl year of 1936. But so far this September, the ratio of high temperature records to low temperature records has been close to 1-to-1. There were 283 daily high temperature records set during the first sixteen days of September, and 246 low temperature records. Eight of the first sixteen days of September have seen the lows outnumber the highs, and eight have seen the highs outnumber the lows. The latest 2-week forecast from the GFS model shows a continuation of pretty normal weather over the U.S. for the rest of the month, and September temperatures will end up close to average.
Jeff Masters
Reader Comments
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Yep North and probably out to sea...here we go...
SURE
well i could see a EWRC taking place which will bump down Roke's wind speed but will allow it to grow larger.
135 hours
moves north 144 hours
Back later if time permits.
Dude, who brought it up? Dr. Masters posted about temperature records. Neapolitan added more data about temperature records.
Then hysterics descended across the blog...
I would think if 98L does not become Tropical Storm before reaching the Islands then it heads South into the Caribbean. Just my take tho.
Seriously, methinks some doth protest too much... ;-)
well. preliminary obs are pointing to another active cyclone season for Qld, and very active fire season for NSW. Today we got a taste of that. Sadly, 3 fires have been confirmed to of been lit deliberately. Btw, thanks.
The nastiness started with Post 17.
Link
agree. it's going to be a mess. although, it is forecast to weaken as it interacts with land and moves north, am wondering about how much nuclear material will get dispersed as it travels past fukushima.
236. PurpleDrank 4:07 PM GMT on September 20, 2011
Totally agree with you Nea. The statements posted regarding any causation inferred from the information you and Dr. JM's provided were completely unwarranted (see #94) and uncalled for.
Nobody said Nea started anything..I myself was talking about the GW discussion period..its not the topic of the blog today..I specifically said Dr. Masters posted about temperature and then here come people who run with it and posts about climate change and whatever..did Nea posts about climate change or GW..no he didnt but his fellow bloggers did and thats who I was pointing at.
uncertainty is a recipe for blog angst.
will check back at 2.
regarding people who annoy you, just iggy and move on. you can only control yourself.
Just a post or two for now.
The models are little or no guidance now as to where 98L may go, assuming it develops which it appears to be doing. It has been essentially sitting in one area for over 24 hours and while quasi stationary or just crawling the rest of the upper air dynamics have been changing to its North and West which affect steering and intensity down the road. For that reason, every time the models run with an initializng position at or close to the same coordinates the extrapolated position out in time will change, sometimes dramatically, from run to run. We see this even when systems are on the move but it is more pronounced when one is going nowehere and everything else is changing around it.
For now the steering is West to just North of West, assuming it starts to head off at an appreciable speed if it is classified later today which seems to be a distinct possibility.
I enjoy hearing about weather events from around the world. thanks Aussie, although I am sad about fires.
Impressive Invest:
Also, the center is much farther north than the NHC thinks.
Blog update:
Tropical Tidbit for Tuesday, September 20th, with Video
thanks Levi very imformative as always
Amen.
We also have to determine just how accurate the old LIG (liquid-in-glass) thermometers were 120 years ago, compared to today's solid state thermistors (which can display in fractions of a degree).
D
Isn't that Maria???
Very extended CFS loop.
3am here, I'm out. Goodnight all.
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