This week could get very interesting in the Eastern Pacific as Hurricanes Hilary and Irwin are expected to interact with each other in a rare phenomenon known as the Fujiwhara effect. Most global models indicate that Hilary, the stronger and larger storm, will be the dominant cyclone and Irwin is likely going to be absorbed into Hilary’s circulation. Meanwhile, Tropical Storm Greg has weakened to a Tropical Depression and is expected to become a remnant low during the next day or two, and there are two other systems worth watching for possible tropical development.

Greg spinning down, likely to become a remnant low on Wednesday or Thursday

Tropical Storm Greg weakened to a tropical depression Tuesday afternoon as it has lost its convective organization due to strong wind shear and dry air. As of 2:00 p.m. PDT (5:00 p.m. EDT), Tropical Depression Greg was centered near 16.2°N 137.9°W and was moving west-northwestward at about 12 mph. Maximum sustained winds were 30 knots (35 mph) with an estimated minimum pressure of 1005 mb. Although convection has increased during the past few hours, Greg’s center is becoming difficult to locate and the cyclone is not well organized. Greg is expected by the National Hurricane Center (NHC) to become a post-tropical remnant low within the next 36 hours as it moves west-northwestward, but it is possible this could occur sooner. Greg is no threat to land. If Greg reaches 140°W before becoming a remnant low, the Central Pacific Hurricane Center (CPHC) will take over advisories.

Hilary has not strengthened as much as expected, but still expected to be the dominant cyclone over Irwin

Hurricane Hilary has strengthened into a Category 2 hurricane today, but has not intensified into a major hurricane like the NHC and most global models predicted. As of 3:00 p.m. MDT (5:00 p.m. EDT), Hurricane Hilary was centered near 15.5°N 108.8°W and was moving west-northwestward at about 12 mph. Maximum sustained winds were 90 knots (105 mph) with an estimated minimum pressure of 974 mb. Hilary is well organized with an eye feature, but the eye is difficult to see on visible satellite imagery. The hurricane is already being affected by some northwesterly shear, and it does not appear likely that Hilary will strengthen much more, if at all. The official NHC forecast predicts that Hilary will continue on a west-northwestward trajectory for the next several days, and the hurricane will be moving into a drier air mass, cooler waters, and increasing wind shear. Hilary will likely begin to weaken later this week due to these less favorable conditions as it begins to interact with Hurricane Irwin. Global models indicate that Irwin could be absorbed into the circulation of Hilary by Day 5.

Irwin likely also peaking in intensity, will likely be absorbed into Hilary

Hurricane Irwin has intensified slightly today as it has developed a small eye feature. As of 2:00 p.m. PDT (5:00 p.m. EDT), Hurricane Irwin was centered near 15.7°N 120.1°W and was moving westward at about 7 mph. Maximum sustained winds were 75 knots (85 mph) with an estimated minimum pressure of 983 mb. Irwin has a small eye occasionally visible on visible satellite in the southeastern part of the Central Dense Overcast (CDO), Irwin could strengthen a little more overnight, but it is likely nearing its peak intensity. Irwin is already being affected by about 10-15 of southerly wind shear, and it is impressive that it has continued to strengthen despite the shear. Irwin is expected to take a dive to the southwest, before eventually turning northward and northwestward as it interacts with Hurricane Hilary. As noted above, Hilary is likely to eventually absorb Irwin and this could occur by Day 5.

Yet another disturbance may develop over Eastern Pacific, possible action in tropical Atlantic next week?

The East Pacific may see one or two more tropical cyclones before quieting down. An area of low pressure is expected to form several hundred miles south of Mexico later this week, and the NHC gives this system a near zero percent chance of development within the next 48 hours and a 30 percent chance within five days. During the next few days, development should be slow, due to strong upper-level winds from nearby Hurricane Hilary. However, conditions could become more favorable by this weekend as it moves westward away from Hilary. In the Atlantic, several global models (GFS, CMC, and UKMET) are hinting at the possibility of an area of low pressure forming over the tropical Atlantic. The Climate Prediction Center (CPC) has indicated a moderate risk of tropical cyclone formation over the Atlantic Main Development Region (MDR) next week, but the NHC has not included it on their Tropical Weather Outlook yet. We will continue to monitor these systems. The next name on the Atlantic naming list is Emily, and the next name on the Eastern Pacific naming list is Jova. I will be back tomorrow with another post on the East Pacific storms as well as the possible Atlantic system.