As is typical for June and July, the eastern Pacific basin is about to get active. The basin already has seen one tropical cyclone – Tropical Depression One-E – form this year, but the eastern Pacific should see its first named storm, Aletta, form this week. Invest 91E currently is given by the National Hurricane Center (NHC) a 60 percent chance of development within 48 hours, and a 90 percent chance of development within five days. There is also a disturbance behind Invest 91E that could develop by late this weekend early next week, and NHC gives this system a 20 percent chance of development within five days.

As of 18:00 UTC Monday, Invest 91E was centered near 11.1°N 103.7°W, and was moving slowly west-northwestward. The associated shower and thunderstorm activity is currently disorganized, but the system is likely to organize into a tropical depression by Thursday. The 12z Monday run of the SHIPS model predicted very favorable conditions for the development of 91E, with wind shear less than 10 knots, sea surface temperatures above 28°C (82.4°F), and mid-level relative humidity values above 70 percent for the next 4-5 days. The only significant inhibiting factor to development is the large size of 91E, which may limit rapid development of the system.

Model support for the development of 91E is nearly unanimous. The 12z Monday ECMWF, GFS, UKMET and CMC models all developed 91E into a tropical depression by late this week. The GFS, UKMET and CMC models are much faster with development, predicting 91E would develop into a tropical depression by Wednesday. The ECMWF model is much slower with development, with the model not predicting genesis until Friday.  The sooner 91E develops, the more likely it is to become a strong hurricane. The GFS model is very bullish on 91E, deepening it into a 941-mb hurricane by early Friday. The ECMWF is much weaker, with only a tropical storm by that time. The environment for 91E is expected to be very conducive, so rapid intensification cannot be ruled out if 91E organizes quickly. 91E should remain far enough west to avoid significant impacts to the western coast of Mexico, although swells are likely along the Pacific coast of North America late this week and into next weekend.

Another disturbance behind 91E

Behind 91E, the models are already predicting another possible tropical cyclone to develop in the eastern Pacific by early next week. The NHC gives this system a near zero percent chance of development within 48 hours, but a 20 percent chance within five days. This system is likely to follow a similar track to 91E, and if 91E becomes a strong hurricane this system may move over the cold wake left by 91E. Interestingly, both the ECMWF and GFS models predict the second system to become a hurricane by the middle of next week. The second name on the eastern Pacific naming list is Bud.

Quiet in the Atlantic

The Atlantic basin is expected to be quiet for the next 10 days and perhaps longer. None of the reliable models are predicting any tropical or subtropical cyclones to form over the Atlantic basin during the next 10 days. This is not surprising, as the month of June averages less than one tropical cyclone in the Atlantic per year. With the eastern Pacific likely to see two named storms over the next 10 days, this will increase wind shear over the Caribbean and Gulf of Mexico, limiting development in the Atlantic basin.

I will be back with an update on the tropics tomorrow.