A low formed to the southwest of Bermuda as forecast. However, it is becoming less likely that it will acquire sufficient tropical characteristics to be classified as a subtropical or tropical cyclone as it drifts northward past Bermuda to the east today. Earlier forecasts suggested that this low would pass to the west of the island bringing a slug of widespread shower activity and strong southeasterly winds for the weekend. However, that forecast evolved through the week and the low passed to the near east of the island overnight Friday into Saturday. This kept that area of widespread showers and strong winds to the east of the island and made for much more settled weather for the weekend with light and variable winds with only an isolated shower at times. Further, the threat for this non-tropical low to acquire sufficient tropical characteristics and become a subtropical or tropical cyclone is diminishing as environmental conditions become increasingly less favorable for that to occur.
Meanwhile, tiny tropical storm Danny strengthened quite stunningly into a major hurricane between Thursday and Friday morning. NOAA P3 Hurricane Hunter Aircraft investigated both the low-level structure of the hurricane and the surrounding upper atmosphere to better assess how conducive the surrounding environment is for Danny’s future. Hurricane Hunter aircraft transmitted some airborne radar data back along with the flight measurements in real time for public dissemination for what could be the first time. Another mission this afternoon will give an updated observational fix on the location and structure of the cyclone and the state of the surrounding environement.
Small hurricanes are often plagued by sudden and extreme swings in intensity. Low vertical wind shear in addition to favorable sea surface temperatures and a pouch of deep tropical moisture that was drawn along with Danny as it pulled northward out of the inter-tropical convergence zone allowed the hurricane to exhibit a burst in intensity that was somewhat greater than expected. The hurricane hunter aircraft found Danny as a category 3 hurricane with roughly 115 mph maximum 1-minute sustained winds and a minimum central pressure near 974 mb.
However, on the flip side, as small cyclones can quickly strengthen under ideal conditions, only slight deviations from ideal conditions can result in a sudden collapse in the cyclone’s convective structure and subsequently rapid weakening. Danny has since weakened from Friday’s intensity and is expected to continue a weakening trend on its approach to the Lesser Antilles Islands.
Despite the jump in strength, Danny is still expected to continue west-northwestward. During this period, an increase in vertical wind shear is expected to allow nearby dry air associated with the Saharan Air Layer to be entrained into the circulation. The dry air forces convection to collapse – this disrupts a tropical cyclone’s circulation and results in weakening. By Monday morning, Danny is expected to be a moderate tropical storm on the doorsteps of the northernmost Lesser Antilles Islands where Tropical Storm Watches are in effect. Danny should then pass near or north of the Virgin Islands and then Puerto Rico Monday night into Tuesday morning – continuing to weaken. Past Tuesday morning the fate of Danny is very uncertain.
Danny could succumb to the vertical wind shear, subsequent dry air entrainment, and land interaction and degenerate into a tropical wave before getting near or north of Hispaniola where environmental conditions begin to improve – the remnant tropical wave would likely dissipate if it were inland over the Dominican Republic or Haiti. Alternatively, Danny could maintain enough of a low level circulation to begin regenerating if it gets north of Hispaniola and avoids significant land interaction. For this reason we cannot rule out that Danny could become a threat to the Turks and Caicos Islands, the southeastern Bahamas Islands on Wednesday and Thursday, or possibly even Bermuda in the following week. It is therefore imperative that constant vigilance be paid to the official products from the Bermuda Weather Service and the National Hurricane Center as the forecast progresses, new information is processed, and confidence in Danny’s ultimate fate increases.
Elsewhere in the Atlantic, a robust tropical wave has moved off the west coast of Africa and is showing signs of early organization near the Cape Verde Islands. This wave has been given a 60% chance of becoming a tropical cyclone in the next 5 days by the National Hurricane Center. This wave is forecast to become a much larger cyclone than Danny, but track westward or west-northwestward into the central tropical Atlantic similar to Danny. Another tropical wave, still inland over Africa also has potential to develop once it emerges into the far eastern Atlantic. Both of these systems will be far out to sea for at least the next five days, and likely past that and so neither of them are immediate threats and there is plenty of time to monitor them.