Tropical Depression Four-E forms, disturbance behind it likely to form as well
Tropical Depression Four-E has formed in the East Pacific, and is headed towards the west-northwest, posing no threat to the coastline of Mexico. As of the latest advisory from the National Hurricane Center, the center of Four-E was located at 13.1N 107.1W, maximum sustained winds were 35 mph gusting to 45 mph, and the barometric pressure remained at 1006 millibars. Visible satellite loops reveal that the tropical depression is fairly disorganized, with the center of circulation in a small burst of convection to the north of the main convective mass. This is due to moderate northerly wind shear that is expected to continue to affect the depression over the next 24 hours or so. If Tropical Depression Four-E intensifies into a tropical storm, it will earn the name "Daniel".
Figure 1. Visible satellite imagery of Tropical Depression Four-E.
The forecast for Four-E
The track forecast for Tropical Depression Four-E remains straightforward. The large, strong area of high pressure responsible for the record June 2012 North American Heat Wave remains in place, preventing the depression from recurving towards the Mexico coastline. This high pressure area is forecast to strength and build westward over the coming days, forcing Four-E on a general west-northwest motion for the next 48 hours before turning more westerly thereafter. In the long range, it is possible that some of the remnant moisture from this cyclone may impact Hawaii, but it is not expected to be well-organized at that time.
Four-E is in a generally favorable environment for further development, characterized by Relative Humidity values near 75% and wind shear below 15 knots, which would typically hinder a cyclone very little. However, because the depression is relatively small and in its formative stages, this is enough to shear it and prevent more quick intensification. The SHIPS model shows wind shear relaxing below 10 knots over the next 24 hours, at which time the system may strengthen more quickly. In fact, the GFS, ECMWF, and HWRF all show a relatively potent tropical cyclone in 72 hours. Shortly thereafter, a slight increase in wind shear and dramatic drop in Sea Surface Temperatures will likely gradually weaken Four-E. My intensity forecast lies a little above the National Hurricane Center's.
...FORECAST POSITIONS AND MAX WINDS...
INIT 04/1800Z 13.1N 107.1W 30 KT 35 MPH
12H 05/0600Z 13.7N 108.2W 35 KT 40 MPH
24H 05/1800Z 14.3N 110.1W 35 KT 45 MPH
36H 06/0600Z 14.8N 112.1W 40 KT 50 MPH
48H 06/1800Z 15.0N 114.3W 55 KT 65 MPH
72H 07/1800Z 15.2N 118.7W 70 KT 80 MPH
96H 08/1800Z 15.5N 123.1W 65 KT 75 MPH
120H 09/1800Z 15.8N 127.4W 60 KT 65 MPH
Elsewhere in the tropics
Global models continue to indicate that another tropical cyclone will form behind Tropical Depression Four-E over the coming days. In fact, many of the models make it a formidable hurricane as it moves west-northwest parallel to the Mexican coastline. The National Hurricane Center is currently giving this suspected disturbance a low chance, 20%, of becoming a tropical cyclone over the next 48 hours. I agree with these percentages.
A tropical wave is moving west-northwestward across the northern Leeward Islands, producing disorganized squally weather over much of the northeast Caribbean Sea. Environmental conditions are not favorable for tropical cyclone development, and the main impacts from this disturbance to the Greater Antilles will be isolated heavy rain and tropical storm-force wind gusts. The National Hurricane Center is currently giving this area a low chance, ~0%, of becoming a tropical cyclone over the next 48 hours. I agree with these percentages as well.
Elsewhere, tropical cyclone development is not expected.