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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This is the only I am going to say... look at 92L... we never thought a storm at 7N.. then remember this
i see it too, it appears to be a very small but compact disturbance
more like wnw, but jogging to the west, systems wobble a lot
look at that wave to the east of 92L...
Uptown, New Orleans, Louisiana (PWS)
Updated: 2 min 39 sec ago
Mostly Cloudy
89.4 °F
Mostly Cloudy
Humidity: 72%
Dew Point: 79 °F
Wind: Calm
Wind Gust: 3.6 mph
Pressure: 30.09 in (Falling)
Heat Index: 105 °F
Visibility: 7.0 miles
UV: 3 out of 16
Pollen: 4.40 out of 12
Pollen Forecast new!
Clouds:
Scattered Clouds 2000 ft
Mostly Cloudy 25000 ft
(Above Ground Level)
Elevation: 20 ft
3 days ago. Can only wait and see!
Statement as of 2:58 AM CDT on June 14, 2010
... Heat advisory remains in effect until 7 PM CDT this evening...
A stagnant area of high pressure will persist through this
afternoon. This will allow afternoon high temperatures to climb
into the low to mid 90s. These hot temperatures combined with
high humidity levels will yield in heat index readings from 104 to
108 degree range this afternoon across much of east central and
southeast Louisiana as well as coastal Mississippi. Warmer urban
areas may see the heat index rise to near 110 degrees.
This area of high pressure aloft is expected to drift north
tonight and allow deep moisture to move in from the south. An
increase in rain chances and slightly lowered high temperatures will
provide a little relief from the heat Tuesday through the weekend.
However... heat index values around 100 degrees will be common each
day across southeast Louisiana and southern Mississippi Tuesday
through the weekend. Precautionary measures are suggested at heat
index values around 100 degrees.
Precautionary/preparedness actions...
The heat index is a measure of how hot it feels when the effects
of humidity are combined with the temperature. A heat index of
105 degrees is considered the level where many people begin to
experience extreme discomfort or physical stress. The heat index
is measured under shady conditions... and direct exposure to
sunlight can increase the heat index as much as 15 degrees.
A heat advisory means that a period of hot temperatures is
expected. The combination of hot temperatures and high humidity
will combine to create a situation in which heat illnesses are
possible. Drink plenty of fluids... stay in an air-conditioned
room... stay out of the sun... and check up on relatives and
neighbors.
DOWNCASTER! J/K:)
Looks like a Tropical Depression, but it seems they are waiting for persistence.
The next three hours of satellite imagery will confirm or refute this
LOL. Sorry for wrong link !.
What crystal ball you using?
BAMs are derived from the GFS, as described in the Technical Summary of the National Hurricane Center Track and Intensity Models. SHIPS shear is always from the GFS model, regardless of the model it is using for track.
THIS IN NO WAY RESEMBLES a Tropical Depression!
Statement as of 10:46 AM EDT on June 14, 2010
... Heat advisory remains in effect until 8 PM EDT this evening...
A heat advisory remains in effect until 8 PM EDT this evening.
Temperatures will climb into the upper 90s to around 100 degrees
in many areas this afternoon. During the peak heating this
afternoon... the dew points will be mainly between 70 and 75
degrees. The combination of these hot temperatures and the
resulting humid conditions will produce heat indices from 105 to
110 degrees for the entire area inland from the intracoastal. A
few places could even experience heat indices near 112 degrees
this afternoon.
Along the immediate shore the heat index values will be a bit
lower as the afternoon sea breeze develops. But little relief
will be found near the ocean as despite temperatures only near
90... the humidity levels will be higher.
Precautionary/preparedness actions...
A heat advisory means that a period of very hot temperatures can
be expected. The combination of heat and humidity will create a
situation in which heat illnesses are possible.
People are encouraged to drink plenty of water... stay out of the
sunshine... check up on the elderly and stay in an air conditioned
location if possible. It is imperative that you do not leave
children or pets in the car... as this can prove deadly in a short
amount of time.
Good morning everyone.
Storm, I just woke up and loaded ONE visible satellite loop. Would you please tell me why this isn't a tropical depression yet?? I don't understand what more the NHC can want here.
I agree that it is expanding to the N. Whether it wraps around to the NW and West remains to be seen.
I agree with you.. a few models were on that, it was suppose to come off much more to the west or back up into the EPAC..nothing more at the surface than a trough not as near along as 92L or anything but I'll give it an outside chance & a definitely bears watching.
In all reality, its based on a technicality. Once they get those T numbers up to 1.5-2.0 from both agencies it will be. Just a half point increase from each agency would warrant an upgrade.
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