The latest forecast from the National Hurricane Center continues to shift the forecast cone toward the Gulf of Mexico. Potential Tropical Cyclone Nine is – apparently – in no rush to fully develop. Though it is in a hurry to get where it is going. The system is still moving to the west-northwest at more than 20mph.
From the NHC
More of the forecast cone from the NHC includes the Gulf of Mexico as the track for PTC9 / Isaias continues to shift to the west.
SUMMARY OF 1100 AM AST…1500 UTC…INFORMATION
LOCATION…15.8N 63.7W
ABOUT 150 MI…240 KM SSE OF ST. CROIX
ABOUT 240 MI…385 KM SE OF SAN JUAN PUERTO RICO
MAXIMUM SUSTAINED WINDS…45 MPH…75 KM/H
PRESENT MOVEMENT…WNW OR 290 DEGREES AT 23 MPH…37 KM/H
MINIMUM CENTRAL PRESSURE…1006 MB…29.71 INCHES
DISCUSSION AND OUTLOOK
At 1100 AM AST (1500 UTC), the disturbance was centered near latitude 15.8 North, longitude 63.7 West. The system is moving toward the west-northwest near 23 mph (37 km/h), and this general motion with a reduction in forward speed is expected over the next few days. On the forecast track, the system will move near or just south of Puerto Rico later today and tonight, near or over Hispaniola on Thursday, and near or over eastern Cuba on Friday.
Maximum sustained winds are near 45 mph (75 km/h) with higher gusts. Some increase in strength is forecast through tonight, with weakening likely on Thursday due to land interaction. Some restrengthening is possible by this weekend.
Environmental conditions are expected to be conducive for additional development, and a tropical storm is forecast to form later today or tonight.
* Formation chance through 48 hours…high…90 percent
* Formation chance through 5 days…high…90 percent
Tropical-storm-force winds extend outward up to 275 miles (445 km) primarily to the north and northeast of the center.
The estimated minimum central pressure is 1006 mb (29.71 inches).
HAZARDS AFFECTING LAND
WIND: Tropical storm conditions are moving across portions of the Leeward Islands and will spread across the U.S. and British Virgin Islands and Puerto Rico this afternoon through Thursday morning. These conditions are forecast to reach portions of the Dominican Republic and Haiti within the warning area early Thursday, and the southeastern Bahamas and Turks and Caicos Thursday afternoon. Tropical storm conditions are possible in the watch areas on Thursday and Friday.
RAINFALL: The disturbance is expected to produce the following rain accumulations:
— Across the northern Leeward Islands, British and U.S. Virgin Islands: 3 to 6 inches.
— Across Puerto Rico: 3 to 6 inches, with isolated maximum totals of 10 inches.
— Across the Dominican Republic, northern Haiti, and Turks and Caicos: 3 to 6 inches, with isolated maximum totals of 8 inches.
— Across the Inagua Islands: 4 to 8 inches, with isolated totals of 12 inches.
These rainfall amounts may lead to life-threatening flash flooding and mudslides, as well as potential riverine flooding beginning today. Urban and small stream flooding is expected for the U.S. Virgin Islands and eastern Puerto Rico.
SURF: Swells generated by Potential Tropical Cyclone Nine will be affecting portions of the Leeward Islands, the Virgin Islands and Puerto Rico during the next day or two. These swells are forecast to reach the north coast of the Dominican Republic, the Turks and Caicos Islands and the southeastern Bahamas tonight or Thursday. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office.
FORECAST POSITIONS AND MAX WINDS
INIT 29/1500Z 15.8N 63.7W 40 KT 45 MPH…POTENTIAL TROP CYCLONE
12H 30/0000Z 16.9N 66.4W 45 KT 50 MPH…TROPICAL CYCLONE
24H 30/1200Z 18.5N 69.8W 50 KT 60 MPH
36H 31/0000Z 19.9N 73.0W 40 KT 45 MPH…INLAND
48H 31/1200Z 21.4N 76.0W 40 KT 45 MPH…NEAR COAST
60H 01/0000Z 22.7N 78.3W 40 KT 45 MPH…OVER WATER
72H 01/1200Z 23.8N 80.2W 45 KT 50 MPH
96H 02/1200Z 26.3N 82.6W 45 KT 50 MPH
120H 03/1200Z 29.0N 83.5W 45 KT 50 MPH
Model Data
The model data continues to be difficult to fully trust due to the slow development of PTC9 / Isaias. Since there is no discernible center, the models have a difficult time plotting the center of the storm within the dataset. And because of that, it means the models have a difficult time making an accurate forecast.
That said, what we can do is look at model trends – not specifics – to get an idea of what may eventually evolve.
And we can start with the European Ensembles.
The above map from Alan Brammer shows the most likely area where PTC9 / Isaias will be during the next seven days. A bulk of the time is spent near or over land. That is a trend I’ve seen within the modeling during the last 36 hours.Many models take PTC9 / Isaias over many of the islands in the Caribbean. This would help keep the system disorganized and weaker.
That track is echoed by the spaghetti models. Notice how many of the lines are over or near land during the trek to the west-northwest and toward the Gulf.
The result is models suggesting a lower “top-end” for strength with this system.
Most of the models are showing that PTC 9 only reaches Tropical Storm of Category 1 Hurricane strength.
Now is that a guarantee? No. Not by a long shot.
But a lower top-end strength is something that has been trending recently within the model data guidance.
Even the SHIPS model guidance is showing the chance for Rapid Intensification is a bit lower today – and through the next 72 hours – than it showed during the past 48 hours. And that has been the trend there, too.
The Bottom Line
I’m encouraged to see that the official forecast from the NHC and the guidance from the model data keep PTC9 / Isaias as a weaker system. Encouraged, but not convinced. There is still a lot of space for this forecast to change. And should it remain disorganized and continue to track more westward than northwestward, the eventual potential strength may become more of a wildcard.
For now, please continue to keep tabs on the forecast and check in on the status of this system daily. Until it forms, and the models can get a good look at where it may be going and how strong it may be, we are still in a bit of a “holding pattern” waiting to figure things out.
