Sunday morning, Hurricane Eugene rapidly intensified to the first major (category 3+) hurricane of not only the 2017 Pacific hurricane season, but the first of the year in all of the Northern Hemisphere. However, Eugene has almost certainly peaked in intensity, and a weakening trend has likely already begun. Meanwhile, in the Atlantic, the National Hurricane Center (NHC) has mentioned a tropical wave in its tropical weather outlook that could develop by late this week as it approaches the Lesser Antilles. The remnants of Tropical Depression Four also are worth watching for regeneration, which is an unlikely scenario but is not out of the question.

Eugene: the strongest tropical cyclone in the Northern Hemisphere so far in 2017

Hurricane Eugene intensified far more than expected and became a category 3 hurricane on the Saffir-Simpson Scale Sunday morning. Maximum sustained winds peaked at 100 knots (115 mph) with a minimum pressure of 965 mb. Eugene was able to take advantage of very light wind shear and warm waters, which allowed it to rapidly intensify. Eugene exceeded nearly all of the intensity guidance, in addition to exceeding both the NHC’s prediction of a category 1 peak and Cyclonic Fury’s prediction of a category 2 peak.

As of 2:00 p.m. PDT (5:00 p.m. EDT), Eugene was centered near 16.7°N 115.3°W and was moving northwest at about 12 mph. Maximum sustained winds were estimated at 100 knots (115 mph) with an estimated minimum pressure of 965 mb. Since that time, Eugene’s eye has become cloud-filled and convective cloud tops have been warming. As a result, the Automated Tropical Cyclone Forecast (ATCF) system has its 00:00 UTC “best track” intensity at 90 knots (105 mph), meaning Eugene will likely be downgraded to a category 2 hurricane at the next advisory. Eugene is currently crossing the 26°C (78.8°F) isotherm, the typical threshold for tropical cyclone development. While wind shear is expected to remain very light (less than 10 knots), rapidly cooling sea surface temperatures and the cyclone entering a drier environment should induce a rapid weakening trend. Eugene should fall below hurricane strength by Tuesday, and the deep convection associated with the hurricane will likely slowly erode until all that is left is a swirl of low clouds. Eugene is likely to become a post-tropical remnant low on Wednesday. The hurricane should continue on its northwestward motion, and should not pose a threat to land other than high swells along the western Mexican coast.

NHC gives African tropical wave a low chance of development

A vigorous tropical wave is located south of the Cape Verde Islands, with plenty of spin and scattered moderate convection. This wave has a chance to develop into a tropical cyclone later this week as it approaches the Windward Islands, moving westward at about 15-20 mph. The NHC currently gives this wave a near zero percent chance of development within 48 hours, and a 20 percent chance of development within five days. The 18z Sunday GFS and GFS Parallel model runs, in addition to the GEFS ensembles, predicted that this wave would likely develop into a tropical depression by Wednesday or Thursday as it nears the Windward Islands. The operational GFS is much faster with development and shows the possibility of a tropical depression forming as soon as Tuesday, while the GFS Parallel is slower with development and weaker. The operational GFS has predicted this wave could strengthen into a hurricane in the eastern Caribbean Sea, and could pose a possible threat to the United States in the long range. However, the 12z UKMET, ECMWF, and CMC models did not predict any development with this wave at all. The ECMWF model predicts that the wave will be too close to the coast of South America to develop. I believe the GFS scenario is highly overdone, and if development occurs I expect a more southerly track closer to South America and weaker in intensity.

The major factor I believe that will determine whether this wave develops or not is its forward speed. If its forward speed is too fast, it will likely not be able to gain latitude and develop into a tropical cyclone, and will struggle to close off a circulation. If the forward speed is slow enough, a tropical depression or storm could form just east of the Windward Islands and emerge into the Caribbean Sea. Another highly uncertain factor is the strength of the wind shear in the Caribbean. Wind shear in the Caribbean is currently quite strong at 40-50 knots (45-60 mph), and it will need to die down quite a bit to support development. I give this tropical wave a 50 percent chance of development within the next ten days, but it is still very possible that this wave interacts too much with the coast of South America to even develop at all. Also, it should be noted that it is still July, not September, and this time of year the eastern Caribbean is usually hostile for tropical cyclone development. Regardless, this wave is worth watching, and I will be posting about it as long as it remains a threat. The next name on the Atlantic naming list is Don, and the next invest number is 95L.

Don’t count out the remnants of Tropical Depression Four

The remnants of Tropical Depression Four continue to produce disorganized showers and thunderstorms north of the Leeward Islands, although the system currently lacks a well-defined circulation. While the NHC has not mentioned this system on their Tropical Weather Outlook, it is worth monitoring for possible regeneration. Several 12z Sunday EPS ensemble members indicated the possibility of this system to regenerate into a tropical cyclone, in addition to the 12z Sunday UKMET model. The remnants of Four should continue on a northwestward motion and be near the Bahamas early this week. Wind shear is expected to be light (less than 10 knots) in the Bahamas, although some dry, stable air could arrest development. The ECMWF and UKMET models predict that the remnant energy of Four will track through the Florida Straits and emerge into the northeastern Gulf of Mexico in about six days. The UKMET model predicts that Four will regenerate here into a tropical storm, while the ECMWF just depicts a broad low pressure area. With shear expected to remain low, this system will have to be monitored despite not much model support.

I will be back tomorrow for an update on these three systems.