Unusually well-organized 92L disturbance may become a tropical depression
Invest 92L, a remarkably well-developed African tropical wave for so early in the season, is midway between Africa and the Lesser Antilles Islands. Infrared satellite loops show a modest area of heavy thunderstorms along the north side of 92L's center of circulation, and the storm's heavy thunderstorms activity appears to be slowly increasing in intensity and areal coverage. Upper-level outflow is apparent to the west and north of 92L, and the outflow has been gradually improving this morning. Visible satellite loops do not show much in the way of low-level spiral bands, and my current take from the satellite imagery is that 92L is slowly organizing, and will not become a tropical depression any earlier than 11pm EDT tonight (Monday.) A 4:27 am EDT pass from the WINDSAT satellite saw a partially closed circulation at the surface (open on the south side), with top surface winds of 25 - 30 mph north of the center.
Figure 1. Morning satellite image of Invest 92L (left side of image) and a vigorous new tropical wave that has moved off the coast of Africa (right side.) None of models develop the new tropical wave, but it bears watching.
Sea surface temperatures
Climatology argues against development of 92L, since only one named storm has ever formed between Africa and the Lesser Antilles Islands in the month of June--Tropical Storm Ana of 1979 (Figure 2). However, sea surface temperatures (SSTs) underneath 92L are an extremely high 28°C, and will increase to 29°C by Thursday. In fact, with summer not even here, and three more months of heating remaining until we reach peak SSTs in the Atlantic, ocean temperatures across the entire Caribbean and waters between Africa and the Lesser Antilles are about the same as they were during the peak week for water temperatures in 2009 (mid-September.)
Dry air not a problem for 92L until Wednesday
The disturbance doesn't have to worry about dry air today or Tuesday--Total Precipitable Water (TPW) loops show a very moist plume of air accompanies 92L, and water vapor satellite loops show that the center of 92L is at least 200 - 300 miles from any substantial areas of dry air. As 92L continues to push northwest, though, the SHIPS model is predicting that relative humidity at middle levels of the atmosphere will fall from the current value of about 70%, to 60% on Wednesday. This dry air may begin to cause problems for 92L on Wednesday, especially since wind shear will be increasing at the same time. Tropical cyclones are more vulnerable to dry air when there is substantial wind shear, since the strong winds causing the shear are able to inject the dry air deep into the core of the storm.
Madden-Julian Oscillation
The 60-day cycle of enhanced thunderstorm activity called the Madden-Julian Oscillation is currently favoring upward motion over eastern tropical Atlantic, and this enhanced upward motion helps create stronger updrafts and higher chances of tropical cyclone development.
Figure 2. Tropical Storm Ana of 1979 was the only June named storm on record to form between Africa and the Lesser Antilles Islands.
Wind shear
A major issue for 92L, like it is for most June disturbances, is wind shear. The subtropical jet stream has a branch flowing through the Caribbean and tropical Atlantic north of 10° N that is bringing 20 - 40 knots of wind shear to the region. Our disturbance was located near 10°N, 40°W at 8am EDT this morning, a few hundred miles south of this band of high shear, and is currently only experiencing 5 - 10 knots of shear. This low amount of shear should allow for some steady development of 92L over the next two days as it tracks west-northwest or northwest at 15 mph. The latest run of the SHIPS model is predicting the shear will rise to 20 knots on Wednesday, which may start to cause problems for 92L.
The forecast for 92L
The National Hurricane Center is giving 92L a high (60% chance) of developing into a tropical depression by Wednesday morning, which is a reasonable forecast. The odds of development have increased since yesterday, as the storm has moved considerably to the northwest, away from the Equator. Now it can leverage the Earth's spin to a much greater degree to help get it get spinning. It is quite unusual for a tropical depression to form south of 8°N latitude.
I expect that 92L's best chance to become a tropical depression will come on Tuesday, and the storm could strengthen enough by Wednesday to be named Tropical Storm Alex. The farther south 92L stays, the better chance it has at survival. With the system's steady west-northwest movement this week, 92L will probably begin encountering hostile wind shear in excess of 20 knots by Wednesday, which should interfere with continued development. Several of our reliable models do develop 92L into a tropical storm with 40 - 55 mph winds, but all of the models foresee weakening by Thursday or Friday as 92L approaches the Lesser Antilles Islands and encounters high shear and dry air. I doubt 92L will be anything stronger than a 45 mph tropical storm when it moves through the northern Lesser Antilles Islands on Friday and Saturday, and it would be no surprise if wind shear has destroyed the storm by then. However, as usual, surprises can happen, and the GFS and the SHIPS model (which is based upon the GFS) do indicate that more modest levels of wind shear in the 15 - 20 mph range late this week may allow 92L to stay stronger than I'm expecting. Residents of the islands--particularly the northern Lesser Antilles--should follow the progress of 92L closely, and anticipate heavy rains and high winds moving through the islands as early as Thursday night.
Oil spill wind forecast
There is little change to the oil spill wind forecast for the coming two weeks. Light winds of 5 - 10 knots mostly out of the south or southeast will blow in the northern Gulf of Mexico all week, according to the latest marine forecast from NOAA. These winds will keep oil near the coast of Louisiana, Alabama, Mississippi, and the extreme western Florida Panhandle, according to the latest trajectory forecasts from NOAA and the State of Louisiana. The long range 8 - 16 day forecast from the GFS model indicates a typical summertime light wind regime, with winds mostly blowing out of the south or southeast. This wind regime will likely keep oil close to the coastal areas that have already seen oil impacts over the past two weeks.
Jeff Masters
Reader Comments
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They better make an app to fix that.
5-day plot - Wind Direction Wind Direction (WDIR): NE ( 50 deg true )
5-day plot - Wind Speed Wind Speed (WSPD): 1.9 kts
5-day plot - Wind Gust Wind Gust (GST): 3.9 kts
5-day plot - Wave Height Wave Height (WVHT): 1.0 ft
5-day plot - Dominant Wave Period Dominant Wave Period (DPD): 6 sec
5-day plot - Average Period Average Period (APD): 5.2 sec
5-day plot - Mean Wave Direction Mean Wave Direction (MWD): S ( 172 deg true )
5-day plot - Atmospheric Pressure Atmospheric Pressure (PRES): 30.01 in
5-day plot - Pressure Tendency Pressure Tendency (PTDY): +0.00 in ( Steady )
5-day plot - Air Temperature Air Temperature (ATMP): 88.3 °F
5-day plot - Water Temperature Water Temperature (WTMP): 92.7 °F
5-day plot - Dew Point Dew Point (DEWP): 75.9 °F
5-day plot - Heat Index Heat Index (HEAT): 99.3 °F
African wave will likely get a mention if this keeps up. IIRC shear's going to lesson, so this actually has a better chance than 92L. 92L has a chance still, never RIP a system until its really dead. We've all learned in the past what happens.
Nothing comparable with an atomic bomb.. but maybe a sign af stronger pop corns later
Yes, the name Chris comes to mind. 2006? I think. The storm that wouldn't die.
iPad is great, it's just a pity we can't run any loop on it :(
what a concept!
Oh, was he meaning he can't post pictures to this site from an iPad because the "Image" tab isn't there?
Absolutely. It amazes me that there are still a few posters on this blog who declare R.I.P. too quickly.
are you really jfv. ha. ha.
Actually I just got atomic web, it supports images. Safari didn't show the image tab.
What on earth do you think I meant by SAL and fast trade winds?
12N 42W seems to show little action convection-wise.
agree 100%
Was it Fred? I remember the storm but cannot remember the name.
and you're such a gracious winner...feel better now?
May I ask where is Hialeah?
miami fla.
You're missing it. SAL and dry air that I'm talking about are synonymous. SAL is dry air. Fast trade winds blow dry air off of Africa. That was 2007's biggest problem.
Hialeah aka "La ciudad que progresa" (the city that progresses) is located in north-central Miami-Dade County FL. lol
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