Invest 98L spinning up; outlook for remainder of hurricane season
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 spin. An ASCAT pass from 8:08 pm EDT last night showed 98L was close to closing off a 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 depression, but most of them do show some weak development. NHC gave the disturbance a 60% chance of developing into a tropical depression by Wednesday in their 8 am Tropical Weather Outlook. Given the recent increase in spin on visible satellite images and favorable environment for development, I'd bump these odds up to 70%. 98L is currently moving little, but is expected to begin a westward motion at 10 mph today. This motion would take 98L into the Lesser Antilles Islands by Friday or Saturday. The northern Lesser Antilles would be most likely to see the core of the storm, as has been the case for all of this year's disturbances. However, a more southerly path across Barbados, as predicted by the GFS model, cannot be ruled out. Once 98L does reach the Lesser Antilles, all of the models indicate the storm will see a sharp increase in vertical wind shear 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.
Atlantic hurricane outlook for the rest of September
Ocean temperatures are starting to decline in the North Atlantic, though remain much above average in the Main Development Region (MDR) for hurricanes, from the coast of Africa to the coast of Central America, between 10°N and 20°N latitude. The latest departure of sea surface temperature (SST) from average plot (Figure 2) shows a large area of ocean temperatures near 1°C above average. The water temperatures were 0.8°C above average in this region during August, which is the 4th highest such reading on record. These warm waters will allow for an above-average chance of African tropical waves developing through early October. By early October, the African Monsoon typically begins to wane, spawning fewer tropical waves that tend to be weaker, and we should stop seeing development of newly-emerged tropical waves off the coast of Africa.
Figure 2. Departure of sea surface temperature (SST) from average for September 19, 2011. Ocean temperatures were about 1°C above average over much of the Main Development Region (MDR) for hurricanes, from the coast of Africa to the coast of Central America, between 10°N and 20°N latitude. In the Pacific off the coast of South America, we can see the tell-tale signature of a La Niña event, with cooler than average waters along the Equator. Also note the cooler than average waters between Bermuda and Puerto Rico, due to the passage of Hurricane Maria and Hurricane Katia. Image credit: NOAA/NESDIS.
Wind shear has been near average over the tropical Atlantic this hurricane season, and is currently at its climatological low point, which occurs in mid-September. The latest 2-week run of the GFS model shows wind shear will remain at the sort of typical low levels we usually see this time of year. With ocean temperatures at near-record warm levels, this combination would tend to favor formation of at least two tropical storms between now and the beginning of October. One inhibiting factor, though, may be the continued presence of dry, stable air over the tropical Atlantic. Hurricanes like to have an unstable atmosphere, with moist, warm air near the surface, and cold, dryer air aloft. This situation helps the updrafts in the storm grow stronger. This year, we've had unusually stable air (Figure 3.) This has really put the brakes on intensification of most of the tropical storms that have formed. The current ratio of 14 named storms but only 3 hurricanes is unprecedented in the historical record, going back to 1851. Usually, just over half of all Atlantic tropical storms intensify into hurricanes. One other factor to consider, the 30-60 day pattern of increased thunderstorm activity known as the Madden-Jullian Oscillation (MJO), looks like it will have little influence over the coming week. The MJO has been weak all month, and is predicted to stay weak for the remainder of this week.
Figure 3. Vertical instability, as measured by the difference in temperature near the surface to the bottom of the stratosphere. The atmosphere in the Caribbean (left) and tropical Atlantic between Africa and the Lesser Antilles Islands (right) has been much more stable than average this year (average is the thick black line). Image credit: NOAA/CIRA.
Forecast of the rest of hurricane season
We are past the half-way point of the Atlantic hurricane season, which typically peaks on September 10. On average, about 60% of the activity has occurred by this point in the season. Since we've already had 14 named storms and 3 hurricanes, at the current rate, we would expect to see another 8 or 9 named storms, with 1 or 2 of them reaching hurricane strength. It's pretty tough to maintain the sort of activity levels we've seen so far this year, so I am forecasting we'll see 7 more named storms during the remainder of this season, taking us all the way to "W" in the alphabet. With the unusually stable air over the Atlantic showing no signs of abating, I predict that we'll see just 2 of these storms reach hurricane strength. As far as steering currents go, the latest 2-week forecast from the GFS model doesn't show any significant changes to the jet stream pattern we've seen all summer. There will continue to be a parade of troughs of low pressure moving off the U.S. East Coast that will tend to curve any storms northwards and then northeastwards out to sea, once they penetrate north of the Lesser Antilles Islands. This pattern favors strikes on North Carolina and New England, and discourages strikes on Texas. I doubt Texas will see a tropical storm this year given this steering pattern, and considering that Texas' tropical cyclone season tends to peak in late August and early September. It is quite unusual for Texas to have a tropical storm or hurricane this late in the season, so they will probably have to look elsewhere for drought-busting rains.
Jeff Masters
Reader Comments
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I'll do some more of these in the next 7 weeks or so. I will consider requests for entries about specific battles.
My question, what do most on here consider a troll?
You're free to go elsewhere.
There is many weather blogs which is just the same everywhere. Nothing unique with them. We who wants something more for instance both science and weather, will not leave this blog and we are many from different countries who read Jeff Masters blog daily.
I read a very well written post by Nea a few days ago and if some of you missed it, here it is again (hope you don´t mind Nea)
Quote comment 1064/post 1931,
Anyone who makes off the wall comments specifically to cause turmoil. People who are just wrong do not qualify ;-)
Neutral years and La Niña years both generally have active late seasons. Considering we've had both, I wouldn't doubt at least 7 more named storms before the season is up.
I'm going to go with 8 more, or to "Alpha".
LOL Yup! POOF for them. Life is good.
I may not know weather, but I know a troll ;<)
Sure you can ask. My definition of a troll is above. If you make comments that fall within that definition, that is what I consider you.
But I really don't count, so don't get overly concerned.
Thanks.
round 1
90L bust
91L bust
92L bust
93L bust
94L bust
95L becomes ARLENE
96L bust
97L bust
98L be comes BRET
99L be comes CINDY
round 2
90L be comes DON
91L be comes EMILY
92L Absorbed by Gert
93L be comes FRANKLIN
94L be comes GERT
95L be comes HARVEY
96L bust
97L be comes IRENE
98L bust
99L bust
round 3
90L be comes TD 10
91L be comes JOSE
92L be comes KATIA
93L be comes LEE
94L bust
95L be comes MARIA
96L be comes Nate
97L bust
98L ????
99L bust
As Pat Might say....Dere's yer prime example
Just look at their joining dates..
September 6, 2011 Posts: 0 Comments: 7
September 18, 2011 Posts: 0 Comments: 9
Its clear to me that this is the same disgruntled probably banned ex-WU blogger that we've been dealing with all season. How else would they know about the people on this blog, like Levi. That's who most of the trolls are people, someone who slipped up either this season and last season and feeling hurt still because of it.
Now, back to the tropics.
98L is getting its act together, gradually. I do think at this time this will become TS Ophelia. Will 98L become a hurricane? I say it has a 'maybe' 30% chance, my reasoning is that 98L is currently embedded within an area of good shear and high SSTs, which will cause it to strengthen, but the ULL in its way will act to shear 98L as it enters the Caribbean. Point being, it will probably look like Maria by the time it enters the islands.
Models aren't overly enthusiastic about 98L's chances, but do show modest strengthening over the next few days. It appears to me that the models might be under-initializing the current intensity (the ECMWF has been struggling with initialization intensity problems, for example several runs on Irene, Katia and Nate had it way stronger than it really was, where as Bret was too weak)
My, I am impressed! You guys are really INTO this. I mostly lurk for info, YOU obviously have a passion for weather. Keep it up, some of us are learning.
Good catch! Taz has more weather knowledge than many on here- he just doesn't flaunt it. :))
Shouldn't reach the islands until Friday or Saturday..Seems like plenty of time to strengthen, no?
ugh
yup oh the nhc report is out on cindy and they upgradeed it too 70 mph
276. funny enough I have heard of the term ''lurking''...
People are assuming you're a troll because of the personal snips and clear and obvious disgruntled attitude towards several bloggers. That's a giveaway to a lot of people, me included.
Arlene - 70 mph
Bret - 70 mph
Cindy - 70 mph (OFFICIAL)
Don - 50 mph
Emily - 50 mph
Franklin - 45 mph
Gert - 60 mph
Harvey - 65/70 mph
Irene - 120 mph
Jose - 45 mph
Katia - 135 mph
Lee - 60 mph
Maria - 75 mph
Nate - 70 mph
Our science officer Dr Master Spock says there are no enemy vessels on the radar. He says they will spread rumors that we are downcasting.
Do you think Maria will be demoted from 80 mph in some of her advisories?
Incorrect.
There have been little fish storms this season -- Cindy, Ten.
2/15 isn't necessarily "most" of the storms.
No, I do not. She had the appearance of an 80 mph hurricane, IMO.
Not really:
The National Hurricane Center does these things called Tropical Cyclone Reports, in which they can go back and look back over a storm, to decide whether they need to raise or lower the intensity, or leave it the storm.
That is how the storms that were originally tropical storms can be upgraded to hurricanes.
Using ASCAT to determine what could be multiple areas of vorticity is not wise. For one thing, there are too many holes in ASCAT. Second of all, the vort centers don't necessarily have to reflect at the surface. There are several mid-level vort maxes spinning around which will make it difficult to consolidate.
Lee and Irene did enough damage to the CONUS for the season, 2011 will be remembered for that.
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