Isaias forms in the Caribbean
Tropical storm conditions possible here next week

By on July 30, 2020

Isaias this morning. (NOAA satellite image)

(National Hurricane Center)

A cyclone in the Caribbean strengthened into Tropical Storm Isaias overnight and, for now, is on a track to brush past the Outer Banks early next week. The National Hurricane Center said this morning that the forecast is still uncertain, both in terms of strength and where the storm will go. For now, it is forecast to follow the classic track paralleling the curving coastline of the Southeastern U.S.

Here is the Hurricane Center’s 5 a.m. report on July 30:

At 5 a.m. AST, the center of Tropical Storm Isaias was located near latitude 17.2 North, longitude 67.9 West. Isaias is moving toward the northwest near 21 mph (33 km/h), and a west-northwestward to northwestward motion with some decrease in forward speed is expected over the next couple of days. On the forecast track, the center of Isaias will move over Hispaniola late today and near the Southeastern Bahamas by early Friday.

Maximum sustained winds are near 60 mph (95 km/h) with higher gusts. Little change in strength is anticipated until landfall in Dominican Republic later today, with re-strengthening forecast on Friday and Saturday.

Tropical-storm-force winds extend outward up to 415 miles (665 km) from the center. A Weatherflow station in Yabucoa Tanque de Agua reported sustained winds of 52 mph (83 km/h) with a gust to 59 mph (94 km/h).

The estimated minimum central pressure is 1003 mb (29.62 inches).

Isaias is sending some mixed signals. The 1-min rapid scan data from GOES-16 indicates that the low-level center is likely displaced west of a very intense burst of deep convection on the northeastern side of the circulation. However, the satellite data also shows increased banding features overnight and a more organized central cloud pattern, with recent hints that perhaps a low-level center is trying to re-form closer to the convection. Radar observations from San Juan show 60-65 kt Doppler wind velocities during the past few hours near 5000 ft, so the initial wind speed is raised to 50 kt.

Model forecasts are showing a complex evolution of the tropical cyclone during the next day or two. There is good agreement that Isaias will move across Hispaniola later today, and its low-level center will likely become disorganized over the high terrain.

However, the strong burst of convection currently near Puerto Rico is associated with a mid-level circulation, which should pass along the north coast of Hispaniola later today. Most of the model guidance suggest that this feature will cause the re-development of a surface center over the northern part of the broader system while the mid-level circulation moves close to the southeastern Bahamas.

Afterward, the cyclone would then move northwestward until the weekend, and gradually turn northward and northeastward close to the U.S. East Coast into early next week ahead of a mid-latitude trough. The official track forecast is a little to the east of the previous one and close to the NOAA corrected dynamical model consensus.

It should be noted that further adjustments to the forecast tracks are indeed possible, especially after Isaias moves north of Hispaniola.

The intensity forecast is quite tricky. In the short term, Isaias is expected to move across Hispaniola, as the storm’s interaction with the mountainous island should cause some weakening and disruption to the circulation. However, as mentioned before, the models suggest that a new center could form, and the environmental conditions would support gradual intensification.

The intensity models have been trending higher, and the official forecast is nudged upward accordingly, now showing a peak intensity of 60 kt when the storm is near the coast of Florida and the Southeast U.S. Coast.

It should be noted that there are models that show hurricane strength near the U.S. but, given the large amount of uncertainty, it is preferred to stay on the conservative side for now. We should have a better idea of how strong Isaias will become near the U.S. after reconnaissance aircraft sample the storm and after it passes Hispaniola later today.



  • Tri-Village

    I know the path is still uncertain. If the storm intensifies and is predicted to hit here Monday through Tuesday I hope the county doesn’t allow visitors to check in on Saturday and issue an evacuation on Sunday. This isn’t tourist bashing or anything of that nature. A lot of prep has to be done before hand and it is difficult to navigate miles of backed up traffic on a two lane road.

    Thursday, Jul 30 @ 9:13 am
  • Avaloner

    In other words, it should be somewhere between a tropical storm and a category 5 by Monday.

    Thursday, Jul 30 @ 1:11 pm
  • Bud

    Finally some good news

    Thursday, Jul 30 @ 4:09 pm