While the eastern Pacific basin remains active, the Atlantic hurricane basin has quieted down after Tropical Storm Don degenerated earlier this week. For the next five days, the National Hurricane Center expects no tropical cyclones to develop anywhere within the Atlantic basin.
While a few tropical waves exist across the basin, none are expected to become a cyclone over the next five days.
The first tropical wave over the eastern Atlantic extends from 17N 31W to 04N 32W, moving west at 20kt. This wave is along the leading edge of a deep pool of moisture off the coast of Africa. Satellite imagery shows an extensive area of Saharan dry air and dust northwest of the wave which will inhibit development.
The second wave, a large amplitude one, is over the central Atlantic with axis from 24N 54W to 08N 55W, moving west at 15 kt. A portion of this wave is forecast to move across the eastern Caribbean during the upcoming weekend, bringing increasing moisture and probabilities for scattered showers and thunderstorms with gusty winds. Even so, no tropical cyclone development is expected here.
The third wave is over the Eastern Caribbean with axis from 19N 64W to 08N 65W, moving west at 20 kt. According to the National Hurricane Center, this wave is capable of producing strong gusty winds as it moves west across the eastern Caribbean today, and across the central Caribbean on Saturday and Saturday night. But as with other waves in the basin, no development is expected of this wave in the coming days.
Lastly, the remnants of former Tropical Storm Don is the last wave being tracked in the basin. Located over the Western Caribbean Sea with an axis from 19N 81W through Panama to the East Pacific at 05N 82W, this wave is producing moderate to strong convection along the coast of Nicaragua. This wave is forecast to move to Central America today, with strong gusty winds and shower and thunderstorm activity likely there.
After a busy few days with a number of named storms in the Pacific and Atlantic hurricane basins, things are slowing down with Tropical Storms Don and Greg and Hurricane Fernanda all weakening.
Overnight, the system that was once Tropical Storm Don degenerated into an open wave. Without an organized tropical cyclone there, the National Hurricane Center will stop issuing advisories on it. An Air Force Reserve reconnaissance aircraft made several passes through the system last night and was only able to find a sharp wind shift–but no winds with a westerly component. With no center of circulation, the National Hurricane Center declared Don an open wave. However, based on the aircraft data, the disturbance is still producing gusty winds of about 35 knots west of the Windward Islands over the far southeastern Caribbean Sea. While this system has degenerated into an open low, residents and visitors of Aruba, Bonaire, and Curacao should continue to monitor this system; heavy showers with gusty winds may occur as the remnants of Don move nearby this week.
In the Pacific, Fernanda is still a hurricane but is weakening. Fernanda’s convective cloud pattern has continued to wither and has been accompanied by a general warming of the cloud tops. The eye is no longer evident in infrared imagery and an analysis early this morning by the National Hurricane Center indicated that the eye had become open in the southern semicircle. Fernanda is forecast to move northwestward today and turn toward the west-northwest by tonight or Thursday. A continuation of that general motion is expected through the end of the forecast period due to a strong subtropical ridge remaining entrenched to the north and northeast of the Hawaiian Islands. As of early this morning (East Coast time), Fernanda was located about 1,330 miles east of Hilo on the Big Island of Hawaii.
Also in the Pacific, Tropical Storm Greg is weakening.Although the initial intensity is a little lower than the previous advisory, the National Hurricane Center says most of the forecast guidance available to them still suggests that Greg will gradually strengthen within a warm sea surface temperature, high-moisture, low-shear environment for the next 24-36 hours. However, Tropical Depression #8 is nearby; if it becomes the dominant cyclone in the area, Greg will dissipate much sooner than currently forecast.
Tropical Storm Don continues to move west, prompting new advisories for the arriving storm. Tropical Storm Warnings are up for Grenada and St. Vincent and the Grenadines. Tropical Storm Watches are up for Barbados, St. Lucia, and now Bonaire.
On its current forecast track, Don could still be a tropical cyclone as it passes near or over Aruba later on Wednesday. Residents and visitors there and elsewhere along the path of this storm should closely monitor it for any changes in strength, forward motion, or direction.
Don’s convective pattern has continued to improve overnight and early this morning, including the development of a pronounced central dense overcast (CDO) feature. There have also been periodic bursts of deep convection very near the center, accompanied by significant clusters of lightning activity, which is indicative of strong updrafts in or near the radius of maximum winds.
According to the National Hurricane Center (NHC), there is no change to the previous track forecast or reasoning. Although the computer forecast models that meteorologists use to aid their forecasting continue to differ some on Don’s forward speed, there is very little cross-track difference. The models are in good agreement that the broad Bermuda-Azores ridge to north of the cyclone will remain strong and move little for the next several days, which should act to keep Don moving briskly westward until dissipation occurs at around 72 hours. The new NHC forecast track is essentially just an extension of the previous advisory track.
Don is expected to remain embedded within a narrow east-west zone of low vertical wind shear for another 24-36 hours, which should allow for some additional strengthening. Since Don is a compact tropical cyclone, significant changes in intensity — both up and down — can occur due to small fluctuations in wind shear and/or interaction
with the mountainous Windward Islands. By 36 hours, increasing westerly shear is expected to cause Don to weaken while it moves across the southeastern Caribbean Sea, and degeneration into an open wave is forecast to occur by 72 hours.
The NHC intensity forecast is similar to the previous advisory and remains below the consensus models ICON and IVCN. However, the intensity guidance continues to vary widely between only showing an open wave (most of the global models) to Don achieving hurricane strength (HWRF, ECMWF, and some of the statistical models). As a result, confidence in the intensity forecast remains low.
Tropical Storm Don, the fourth named tropical cyclone of the 2017 Atlantic Hurricane Season, has formed.
An Air Force Reserve reconnaissance aircraft investigating the area of low pressure located east-southeast of the Windward Islands found a small, but well-defined surface circulation and a small area of tropical-storm-force winds over the eastern semicircle of the circulation. The associated convection is not particularly well organized, but there is a curved band located to the north of the center and a couple of bursts have formed closer to the small circulation center this afternoon. Based on this data, the National Hurricane Center (NHC) declared this system a tropical storm and initiated advisories for it.
According to the NHC, Don is currently within a low shear environment and over warm water, so some strengthening is possible tonight and Tuesday. Once the system enters the eastern Caribbean Sea, strong upper-level westerly winds and strong low-level easterly flow are likely to cause the small circulation to open up into a trough. As a result of that hostile environment, dissipation is forecast within 72 hours.
Nevertheless, stormy conditions could impact Aruba and nearby islands as soon as Wednesday. Residents and vacationers there and elsewhere in the Caribbean in the path of this storm should closely monitor the tropical forecast for any changes.