Tropical Storm Helene Advisory Number 3 NWS National Hurricane Center Miami FL AL082018 1100 PM AST Fri Sep 07 2018 ...TROPICAL STORM HELENE FORMS BETWEEN THE COAST OF AFRICA AND THE CABO VERDE ISLANDS... ...EXPECTED TO BRING TROPICAL STORM CONDITIONS TO PORTIONS OF THE CABO VERDE ISLANDS SATURDAY NIGHT AND SUNDAY. SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION ----------------------------------------------- LOCATION...13.6N 18.5W ABOUT 405 MI...650 KM E OF THE SOUTHERNMOST CABO VERDE ISLANDS MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H PRESENT MOVEMENT...W OR 280 DEGREES AT 12 MPH...19 KM/H MINIMUM CENTRAL PRESSURE...1002 MB...29.59 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: None. SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Tropical Storm Warning is in effect for... * Santiago, Fogo, and Brava A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area within 36 hours. For storm information specific to your area, please monitor products issued by your national meteorological service. DISCUSSION AND OUTLOOK ---------------------- Satellite data indicate that the depression over the far eastern Atlantic has strengthened and is now Tropical Storm Helene. The center of the tropical storm is a little to the east of previously indicated position, and at 1100 PM AST (0300 UTC) was located near latitude 13.6 North, longitude 18.5 West. Helene is moving toward the west near 12 mph (19 km/h), and a westward to west-northwestward motion with a gradual increase in forward speed is expected during the next 72 hours. On this track, Helene will be passing very close to the southern Cabo Verde Islands during Saturday night and early Sunday. Maximum sustained winds are near 40 mph (65 km/h) with higher gusts. Some strengthening is forecast during the next 2 to 3 days, and Helene could become a hurricane early next week. Tropical-storm-force winds extend outward up to 70 miles (110 km). mainly to the south of the center. The estimated minimum central pressure is 1002 mb (29.59 inches). HAZARDS AFFECTING LAND ---------------------- WIND: Tropical storm conditions are expected to first reach the warning area Saturday night or on Sunday. RAINFALL: Helene is expected to produce total rain accumulations of 3 to 5 inches, with maximum totals of 8 inches across the southern Cabo Verde Islands. This rainfall may produce life-threatening flash floods.
Tropical Storm Helene Discussion Number 3 NWS National Hurricane Center Miami FL AL082018 1100 PM AST Fri Sep 07 2018 A very timely ASCAT pass indicated that the winds associated with the depression have increased to 35 kt, and also that the center was a little east of the location previously indicated. This is very common in systems during the formative stage. Based on the ASCAT data, the system has been upgraded to Tropical Storm Helene, the eighth named storm of the season. The satellite presentation has also improved during the past several hours, and now the cyclone has large cyclonically curved convective bands to the south of the center. The outflow is fair in all quadrants. Helene will be moving over warm waters and within an environment of light shear through the next 3 to 4 days, and most of the guidance responds to that environment by gradually strengthening the cyclone. The NHC forecast follows the trend of the intensity consensus, and brings Helene to hurricane intensity in about 3 days. Currently, Helene is embedded within a southwest monsoon-type flow, and is moving toward the west at about 9 or 10 knots. However, as the cyclone moves away from the African coast, it will become steered by the easterly flow around the subtropical ridge and should then increase in forward speed. Most of the track models are in extremely good agreement, at least for the next 3 days when the confidence in the forecast is high. At the long range, a mid-level trough is expected to develop over the central Atlantic, forcing the cyclone to turn more to the northwest and even north later on. The NHC forecast is in the middle of the guidance envelope and basically on top of the corrected consensus HCCA. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 13.6N 18.5W 35 KT 40 MPH 12H 08/1200Z 13.8N 19.9W 35 KT 40 MPH 24H 09/0000Z 14.3N 22.3W 40 KT 45 MPH 36H 09/1200Z 14.8N 25.0W 50 KT 60 MPH 48H 10/0000Z 15.4N 28.0W 55 KT 65 MPH 72H 11/0000Z 17.0N 33.9W 65 KT 75 MPH 96H 12/0000Z 18.5N 39.0W 65 KT 75 MPH 120H 13/0000Z 20.5N 42.5W 60 KT 70 MPH NEXT ADVISORY ------------- Next intermediate advisory at 200 AM AST. Next complete advisory at 500 AM AST.