The Northern Hemisphere tropics are beginning to get active as they typically do in July. The Atlantic, East Pacific and West Pacific all have areas to watch this week. In the Atlantic, a tropical wave is located southwest of the Cabo Verde Islands and is being monitored for gradual development. In the East Pacific, there is potential for two tropical cyclones to form with Invest 94E and another tropical wave. In the West Pacific, Tropical Storm Nanmadol has formed in the East China Sea, and is likely to impact Japan this week.

Atlantic: A Tropical Wave Could Develop During The Next Several Days

A tropical wave located about 650 miles west-southwest of the Cabo Verde Islands could develop into a tropical depression later this week as it moves slowly westward through the Atlantic Main Development Region (MDR) at about 10 mph. The National Hurricane Center (NHC) gives this system a 10 percent chance of development in the next 48 hours, and a 50 percent chance within five days. The 12z Sunday GFS, UKMET, and CMC models all predicted development of this system into a tropical depression by Friday. There was also significant ensemble support with the GEFS and GEPS. This tropical wave is likely to continue on a westward to west-northwestward path during the next several days, and could be near the Leeward Islands by next weekend. Wind shear is fairly light in most of the Atlantic MDR, less than 15 knots, and this could be a positive for development. However, subsidence from the lack of a supportive MJO and Saharan Air Layer (SAL) may limit this wave’s ability to develop in the Atlantic MDR despite otherwise favorable conditions. Sea surface temperatures are currently a marginal 26-27°C (78.8-80.6°F), but are expected to increase to near 28°C by the time the wave is near the Leeward Islands. The GFS model currently predicts that this system will develop into a tropical depression without directly striking the Lesser Antilles, and could be near the Bahamas by early next week. A weakness in the subtropical ridge is likely to cause this system to begin to turn to the northwest without ever entering the Caribbean. The 12z GFS operational run and a few GEFS ensemble members indicate that this system could be a hurricane in the western Atlantic in the long range, but this is still too far out to be taken seriously. Track and intensity forecasting remains very uncertain at this time, since a closed circulation has not yet formed.

The tropical wave is slightly better organized than yesterday, with more thunderstorm activity. However, it still has a ways to go before being designated a tropical cyclone. It is yet to be designated an “Invest” by the NHC. Once a system is designated an invest, it gets model guidance and models generally become more accurate. The next name on the Atlantic naming list is Don. I give this system a 50 percent chance of developing into Tropical Storm Don during the next ten days.

East Pacific: Invest 94E designated, another tropical wave to watch

In the East Pacific, Invest 94E has recently been designated by the NHC this afternoon. As of 18:00 UTC Sunday, 94E was centered near 11.6°N 106.2°W. Maximum 1-minute sustained winds were estimated to be 20 knots (25 mph) with an estimated minimum pressure of 1010 mb. 94E is expected to continue westward in the East Pacific without ever posing a threat to land, although it could enter the Central Pacific in the long range. The NHC gives 94E a 20 percent chance of development within 48 hours, and a 40 percent chance within five days. The 12z Sunday ECMWF run develops this system, while the 12z Sunday GFS does not.

Also in the East Pacific, NHC is monitoring another tropical wave south of Guatemala that could develop. NHC gives this tropical wave a near zero percent chance of development within 48 hours, and a 60 percent chance within five days. The 12z Sunday GFS and ECWMF both develop this system into a tropical depression in about five days. Much like 94E, it does not appear as if this system will pose a threat to land at this time. The next two names on the East Pacific naming list are Eugene and Fernanda.

West Pacific: Tropical Storm Nanmadol forms in East China Sea, not likely to strengthen much

The fifth tropical cyclone and third named storm of the 2017 Pacific typhoon season, Tropical Storm Nanmadol, formed early Sunday in the East China Sea. As of 18:00 UTC Sunday, Nanmadol was centered near 24.7°N 124.0°E, and was moving north-northwestward. Maximum 1-minute sustained winds were estimated to be 45 knots (50 mph) with a minimum pressure of 989 mb. Maximum 10-minute sustained winds are estimated to be 50 knots (60 mph), making Nanmadol a severe tropical storm on the Japan Meteorological Agency (JMA) scale. Nanmadol is likely to curve towards the northeast and could make landfall in Japan as a tropical storm or extratropical storm. Nanmadol is a small storm, and is not likely to strengthen much, if at all, before reaching Japan by Tuesday.

I will be back for another post tomorrow evening on the several tropical systems were are tracking. The Northern Hemisphere tropics are likely going to be active now for much of the rest of the year.