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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Raleigh, I live inland. As a young boy, went through Hugo 1989 in the Appalachian mountains (which I didn't remember but my parents tell me the story) and Fran 1996 while in Raleigh. Even though I don't live at the coast, watching for those storms that charge inland and wreak havoc away from the coast.
Visited the beaches a lot though, particularly Atlantic Beach and Nags Head. Should check out Carolina Beach at the Wilmington area.
It will have a favorable environment ahead of it yes, and as I said in post 1200, some models are developing it, including the ECMWF, so I will be watching it closely.
I don't see anybody forecasting doomsday for the Caribbean from 92L.
Updated: 1 sec ago
Partly Cloudy
103.5 °F
Partly Cloudy
Humidity: 43%
Dew Point: 77 °F
Wind: 4.0 mph from the SW
Wind Gust: 6.0 mph
Pressure: 29.84 in (Falling)
Heat Index: 121 °F
Savannah Hunter, Georgia (Airport)
Updated: 24 min 41 sec ago
Partly Cloudy
101 °F
Partly Cloudy
Humidity: 39%
Dew Point: 72 °F
Wind: 10 mph from the West
Pressure: 29.89 in (Falling)
Heat Index: 110 °F
I've lived my whole life here, and I'm used to the heat... but 101F in June is BONKERS!!!
Well, could you show me why you think the Caribbean will be hostile this season? All signs point towards the opposite.
NATIONAL WEATHER SERVICE CHARLESTON SC
522 PM EDT MON JUN 14 2010
...RECORD HIGH TEMPERATURE SET AT SAVANNAH GA...
A RECORD HIGH TEMPERATURE OF 102 DEGREES WAS SET AT SAVANNAH GA
TODAY. THIS BREAKS THE OLD RECORD OF 100 SET IN 1921.
My poor AC unit can't keep up!!!
No, it weakens but remains over the NE Caribbean tomorrow and doesn't move much. It's not until 48-72 hours when it really starts to lift north.
A bit warmer over there than any of your neighbors:
But no official obs of ~77 F dewpoints. Suspicious...
You are right to use the airport obs, primarily.
Interesting to note that the SHIPS model has backed off on the strength of the subtropical jet stream from yesterday, with Invest 92L only experiencing 20 knots in the 48-60 hour frame before backing down to 14-18 knots thereafter.
Looking at the latest GFS 850mb-200mb shear run, it now suggests the jet stream may begin to lift north in the 48 hour time period (where as yesterday the GFS was suggesting this at 100 hours). Based on low level steering currents, 92L should stay on a general west to westnorthwest motion, and may be able to navigate through more modest shear of 10-20 knots instead of the 20-30 knots currently located to the west and north.
Yea, I am always suspicious of PWS's. You never know if they were set up on a tar roof or above an exhaust vent...
Ok thanks, Its one thing to have the knowledge but another to apply it to the maps...thats what i need to improve on...But Meteorologist are always improving eh
We seem to have dewpoint temps from them much higher than any official obs a lot. This time of year, they always get posted in here, and they usually are way off. I wonder why it seems to be so hard to have a reasonable amount of accuracy in a PWS dew point...how exactly do they measure it? Anyone? (Obviously not a wet-bulb psychrometer)
And some have said things like they might be closer to some water than the airport obs...well if it was down wind of a sizable body of water, then the temps would be moderated a bit. But they aren't.
EDIT: for typos...phone-typing, bad combination
How was it recorded?
(and I'd like to know where...if in situ, prolly shallow water)
That area in the SW GOM is a weak tropical wave interacting with an Upper Level Low. No development in this area is expected.
Link
In JFV's salt water kiddy pool.
I was told that the coastal Carolina SST get nearly this high and often? It came from a naval officer. Not sure it's accurate.
It couldn't have been shallow water or we would have already broken that record today in the northern gulf, which seems unlikely.
I read it off the Wiki page for hypercanes that someone posted earlier. They cite UCAR and this site for the ocean temperature data, and the latter site seems to imply that SSTs of 36C (96.8F) have been observed in the Persian Gulf.
It's Wiki....don't know where to get more specific info.
BETWEEN 55W AND 65W
530 PM EDT MON JUN 14 2010
.SYNOPSIS...A TROPICAL WAVE S OF 16N ALONG 84W WILL MOVE W
THROUGH THE GULF OF HONDURAS TUE. ANOTHER TROPICAL WAVE E OF THE
AREA S OF 17N ALONG 52W WILL REACH ALONG 56W TUE...ENTER THE E
CARIBBEAN WED...AND CONTINUE TO ALONG 75W FRI...AND 80W SAT. A
TROUGH WILL MOVE W TO ALONG 55W THU...ALONG 60W FRI...AND 65W
SAT.
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