Hurricane Fernanda rapidly intensified last night into today to become the strongest tropical cyclone of 2017 so far in the Northern Hemisphere. Fernanda is now a Category 4 hurricane on the Saffir-Simpson Hurricane Scale – the first of such this year. Fernanda was able to rapidly intensify over very favorable conditions, including light wind shear, a moist environment and very warm sea surface temperatures. Some slight additional intensification is possible before eyewall replacement cycles will likely cause fluctuations in intensity beginning tomorrow.

Forecast for Fernanda

As of 2:00 p.m. PDT (5:00 p.m. EDT) Friday, Hurricane Fernanda was centered near 10.7°N 119.7°W and was moving westward at about 12 mph. Maximum sustained winds were estimated at 115 knots (130 mph), with an estimated minimum pressure of 960 mb. The pressure of 960 mb is unusually high for a category 4 hurricane, and is likely due to the low latitude. It is notable that Fernanda was able to rapidly intensify at such a low latitude. Fernanda is a well-organized hurricane, with a distinct, clear eye surrounded by a ring of deep convection.

During the next 36-48 hours, Fernanda is expected to remain in very favorable conditions, with light wind shear of 5-10 knots, relative humidity values of over 70 percent, and sea surface temperatures above 28°C (82.4°F). This could support a little bit more strengthening, but the possibility of eyewall replacement cycles complicates the short-term intensity forecast. The official NHC forecast predicts Fernanda to peak at 130 knots (150 mph). It cannot be ruled out that Fernanda reaches Category 5 status if an eyewall replacement cycle does not begin soon, though this is unlikely. By Day 3, the environment around Fernanda begins to become drier with relative humidity values dropping below 60 percent. This should cause a slow weakening trend to commence thereafter. Sea surface temperatures are also expected to drop below 26°C (78.8°F) by Day 5, along with relative humidity values falling to 40-45 percent. The weakening should become more rapid by that time as Fernanda emerges into the less favorable Central Pacific basin. By next week, it is possible that Fernanda could struggle to maintain deep convection as it moves into the drier environment with cooler water temperatures. This is expected to weaken Fernanda to a tropical storm or perhaps even a remnant low as it nears the Hawaiian Islands in about nine days. The ECMWF model shows Fernanda remaining south of the Hawaiian Islands, while the GFS model shows Fernanda directly striking the Big Island of Hawaii. The Hawaiian Islands should continue to monitor the progress of Fernanda, although it is likely to be weak by the time it is in the area due to the less favorable conditions.

Invest 97E designated in East Pacific, could also develop; Atlantic still quiet

A broad area of low pressure has formed south of the Gulf of Tehuantepec, and has potential to develop into a tropical depression as it moves slowly west-northwestward to northwestward. This area of low pressure has recently been designated Invest 97E by the National Hurricane Center (NHC). The NHC gave 97E a 10 percent chance of development within 48 hours, and a 50 percent chance within five days. The 12z Friday GFS, ECMWF, UKMET and CMC model runs were not very optimistic with development of 97E. As of 18:00 UTC Friday, 97E was centered near 12.5°N 97.0°W, with maximum sustained winds near 25 knots (30 mph) and an estimated minimum pressure of 1009 mb. 97E is expected to be in fairly light shear and warm water temperatures by early next week, when it could develop. However, it is possible that the outflow of Hurricane Fernanda could suppress development by inducing wind shear on 97E. The next name on the East Pacific naming list is Greg.

The tropical Atlantic continues to be quiet, and the NHC still does not expect any new tropical cyclones to form over the next five days. I will be back tomorrow for another post on Fernanda and 97E.