Aside from Hurricane Fernanda, which has weakened slightly from yesterday, the global tropics have lit up today with several systems. In the Atlantic, a trough of low pressure has a low chance to develop into a tropical cyclone as it approaches the Windward Islands by Tuesday. In the Western Pacific, Tropical Storm Talas has developed over the South China Sea, and is likely to strengthen slightly over the Gulf of Tonkin tomorrow. In the Eastern Pacific, Invest 97E is likely to develop into a weak tropical cyclone without posing a threat to land, with another disturbance also having a low chance of development. There is quite a lot to talk about today!

Fernanda weakens slightly due to an eyewall replacement cycle, could restrengthen tomorrow

Hurricane Fernanda over the tropical Eastern Pacific has weakened slightly from yesterday, and its eye is no longer as well defined as yesterday. As of 2:00 p.m. PDT (5:00 p.m. EDT) Saturday, Hurricane Fernanda was centered near 11.4°N 124.0°W, and was moving westward at about 13 mph. Maximum sustained winds were 115 knots (130 mph), with an estimated minimum pressure of 955 mb. This is slightly weaker than Fernanda’s peak intensity last night, with maximum sustained winds of 125 knots (145 mph) and a minimum pressure of 947 mb. The weakening appears to have been caused by an eyewall replacement cycle – a natural process that occurs in strong tropical cyclones that typically results in a temporary weakening. A microwave pass also indicated concentric eyewalls this morning. Since that time, the appearance of Fernanda has not improved, and it is likely that Fernanda will be downgraded to a category 3 hurricane at the next advisory.

In the short term, conditions are favorable for Fernanda to possibly re-intensify slightly tomorrow after the eyewall replacement cycle completes. During the next 48 hours or so, wind shear is expected to remain light (less than 5 knots), along with sea surface temperatures above 27°C (80.6°F) and relative humidity values of 60 percent. By Tuesday, sea surface temperatures begin to slowly decrease as the hurricane enters a much drier and more stable environment. A slow weakening trend is likely to commence at that time. By Day 5, conditions become even more unfavorable as wind shear is expected to increase to above 20 knots (25 mph) along with sea surface temperatures falling to near 25°C (77°F). Global models continue to predict that Fernanda will be near the Hawaiian Islands in eight to nine days. It is likely that by this time the unfavorable conditions will have weakened Fernanda to a weak tropical storm or perhaps even a remnant low. The Hawaiian Islands should continue to monitor the progress of Fernanda.

Tropical Storm Talas forms in South China Sea, expected to make landfall in Central Vietnam

Saturday morning, a broad area of low pressure developed into Tropical Storm Talas over the South China Sea, the fourth named storm of the unusually quiet 2017 Pacific typhoon season. As of 00:00 UTC Sunday, Talas was centered near 17.4°N 109.5°E, with maximum 1-minute sustained winds of 40 knots (45 mph). Maximum 10-minute sustained winds from the Japan Meteorological Agency (JMA) came in slightly higher, at 45 knots (50 mph). Talas’ center of circulation is emerging into the Gulf of Tonkin, and some slight strengthening is possible as it approaches the Vietnamese coast. Due to the broad nature of Talas, land interaction, and limited time over water, it does not seem likely that Fernanda will strengthen into a typhoon. Vietnam, Laos, Cambodia, and Thailand should monitor the progress of Talas.

Low pressure area in tropical Atlantic could develop slightly over next few days

In their 8:00 p.m. EDT Tropical Weather Outlook, the National Hurricane Center (NHC) noted the possibility of a trough of low pressure located over the central tropical Atlantic, associated with a tropical wave, to develop into a tropical cyclone as it approaches the Windward Islands.  The NHC gave this system a 10 percent chance of development within 48 hours, and a 20 percent chance of development within five days. If any development does occur, it would likely be brief, due to strong trade winds and wind shear in the Eastern Caribbean Sea. In addition, some Saharan Air Layer (SAL) to the west of the system could limit development in the short term. The 18z Saturday GFS and GFS-Parallel model runs, as well as the 12z Saturday CMC run, indicated that this system could develop into a tropical cyclone near Barbados by late Tuesday. The 12z Saturday ECMWF run predicted that this system would pass through the Windward Islands as a strong tropical wave. If this system does develop into a tropical cyclone, it would be the earliest fifth tropical cyclone of an Atlantic hurricane season since the hyperactive 2005 Atlantic hurricane season. Barbados, Trinidad and Tobego, and the Windward Islands should monitor the progress of this system. It is possible that it could produce tropical storm conditions even if it does not develop a well-defined circulation. The next name on the Atlantic naming list is Don. This system has not yet been designated an Invest.

Invest 97E likely to become a weak tropical cyclone in Eastern Pacific, low chance of another area of disturbed weather developing

In addition to Fernanda, the Eastern Pacific has two other systems to watch, although neither is likely to become a hurricane. A broad area of low pressure south of Mexico – Invest 97E – is given a 50 percent chance of development within 48 hours, and a 70 percent chance of development within five days, by the NHC. The GFS, CMC, and ECMWF models all indicate the possibility of some slight development with 97E. Wind shear is expected to be moderate, about 15 knots, with the atmosphere being marginally moist with relative humidity values of about 65 percent. Sea surface temperatures are expected to be favorable, above 28°C (84.2°F) for the next few days, before gradually decreasing by Day 4. Unlike Dora, Eugene, and Fernanda, Invest 97E is not likely to become a hurricane due to the less favorable environment. Another system is also given a low chance to develop by the NHC west of 97E, and the NHC gives this area of disturbed weather a 10 percent chance of development within 48 hours and a 20 percent chance within five days. Global models show very little development with this system. The next two names on the Eastern Pacific naming list are Greg and Hilary.

 

I will be back for another post tomorrow on all of these systems. The tropics are getting busy as we get closer to the peak!