A well-defined area of low pressure located along a dissipating cold front in the Northeastern Gulf of Mexico was designated Invest 98L by the National Hurricane Center (NHC) Sunday morning. Aside from 98L, a tropical wave in the central tropical Atlantic is becoming less likely to develop due to dry air. In the Western Pacific, Typhoon Noru explosively intensified to Earth’s first category 5 tropical cyclone of 2017, but has since weakened slightly. In the Eastern Pacific, Hilary has now become a post-tropical remnant low, while Irwin continues to hang on as a tropical storm. There is also a new disturbance that could develop over the East Pacific.

Invest 98L could spin up quickly during the next few days, but likely to remain weak

As of 00:00 UTC Monday, Invest 98L was centered near 28.0°N 84.6°W and was moving slowly southeastward. Maximum sustained winds were 30 knots (35 mph), with an estimated minimum pressure of 1009 mb. 98L currently consists of a somewhat well-defined surface low, but is still attached to a cold front. In order for 98L to develop into a subtropical or tropical cyclone, it will need to detach from the front completely. NHC gives 98L a 20 percent chance of development within 48 hours, and a 30 percent chance of development within five days. I agree with these chances. Although the global models do not show much development with 98L, it is possible that it could briefly spin up into a tropical or subtropical cyclone, perhaps either before landfall in Florida or along the Gulf Stream later this week. Currently, wind shear of over 20 knots is shearing all of the convective activity to the south. Although the shear could decrease slightly tomorrow, it will likely remain too high for significant organization before 98L moves inland into Florida. While sea surface temperatures are very warm at 30°C (86°F), the shear and mid-level relative humidity values of less than 50 percent are working against development. The environment for 98L will not become much more favorable in the long term, but these frontal remnants can spin up fast and need to be watched. It is unlikely that 98L will become anything stronger than a minimal tropical or subtropical storm when it reaches Florida on Tuesday morning. Even if 98L does not develop into a subtropical or tropical cyclone, it could cause tropical storm conditions across parts of Central Florida. After 98L emerges into the Atlantic, most models keep it away from the Eastern United States coast, but the ECMWF model is a western outlier and predicts 98L will be close to the eastern coast of North Carolina by Thursday.

Typhoon Noru explosively intensifies, but weakens a little this evening

Only a severe tropical storm yesterday, Typhoon Noru explosively intensified Sunday to become the first category 5 tropical cyclone of 2017. Located over sea surface temperatures of near 31°C (87.8°F), Noru’s 1-minute maximum sustained winds increased to 140 knots (160 mph) with an estimated minimum pressure of 912 mb at 18:00 UTC Sunday afternoon. This makes Noru the first super typhoon of the 2017 season, as well as the strongest tropical cyclone so far recorded on Earth this year. Noru has since slightly weakened, and maximum 1-minute sustained winds have decreased to 130 knots (150 mph) with the pressure rising to an estimated 922 mb. Maximum 10-minute sustained winds from the Japan Meteorological Agency are much lower, at 90 knots (105 mph). Noru is centered near 22.8°N 140.5°E. The ECMWF model predicts that Noru could be very near central Japan as a strong typhoon by early next week, but the GFS model predicts that Noru will recurve eastward away from Japan. Residents in Japan should monitor the progress of Noru very closely.

Atlantic tropical wave not likely to develop, East Pacific system may develop

A tropical wave located about halfway between the Lesser Antilles and Africa is not likely to develop into a tropical cyclone. In the 8:00 p.m. EDT Tropical Weather Outlook, NHC gave this system a near zero percent chance of development within 48 hours, and a 20 percent chance of development within five days. This was down from the 30 percent chance on Sunday morning. Only the 12z Sunday CMC model predicted development – the more reliable 12z Sunday ECMWF, GFS and UKMET models did not predict any development. Dry air from the Saharan Air Layer (SAL) has limited the convective activity of this wave, and I do not think it is likely to develop into a tropical cyclone. It may even be dropped from the NHC’s Tropical Weather Outlook at 2:00 a.m.

In the East Pacific, an area of cloudiness and showers has developed west of Costa Rica. NHC gives this disturbance a 10 percent chance of development within 48 hours, and a 40 percent chance of development within five days. The 12z Sunday GFS, UKMET and CMC model runs predicted development of this disturbance, while the 12z Sunday ECMWF run did not.

The next name on the Atlantic naming list is Emily, and the next name on the East Pacific naming list is Jova. I will be back tomorrow for a post on 98L.