Although this depression doesn't look like it's going anywhere it reminds me I should probably do a post on the Madden-Julian Oscillation.
From Wunderblog (on blogroll at left):
Invest 91L Bringing Heavy Rains to Florida, Cuba, and Mexico
The Atlantic hurricane season began on June 1, and we already have a threat to discuss. A trough of low pressure has developed over the Western Caribbean, Mexico's Yucatan Peninsula, and Southeast Gulf of Mexico, and is dumping heavy rains over the area. Hurricane Barbara, which died on Thursday as it attempted to cross Mexico's Isthmus of Tehuantepec into the southernmost Gulf of Mexico, has contributed moisture to this disturbance, which has been designated 91L by NHC. Satellite loops show a large area of heavy thunderstorms with poor organization, and there is no evidence of an organized surface circulation trying to form.
Wind shear is a high 30 knots, and is forecast to remain high, 20 - 30 knots, over the next five days, so any development should be slow to occur. NHC is giving the disturbance a 20% chance of developing into a tropical cyclone by Wednesday. The Hurricane Hunters are on call to fly into 91L on Tuesday afternoon, if necessary. Regardless of whether or not 91L develops into a tropical depression, heavy rains will be the storm's main threat. Mexico's Yucatan Peninsula, Western Cuba, and South Florida can expect 5 - 8" of rain from the disturbance over the next four days. Heavy rains from 91L may spread up the U.S. East Cost late this week. The computer models predict that 91L should stay large and poorly organized, and if it does develop, it will be difficult for it to get any stronger than a 45 mph tropical storm in the Gulf of Mexico.
Figure 1. Latest satellite image of Invest 91L.