KNMI: TROPICAL CYCLONE BULLETIN NO. 13

TROPICAL CYCLONE BULLETIN NO. 13

ADVISORY MESSAGE NO. 1

Date: Wednesday September 06, 2017 Time: 09:46 local time

Watches/warnings:

At 1100 AM AST (1500 UTC), the eye of Hurricane Irma was located near latitude 18.2 North, longitude 64.0 West. Irma is moving toward the west-northwest near 16 mph (26 km/h), and this general motion is expected to continue for the next couple of days. As Irma is moving away from the islands now, the wind will pose no further threat to the islands.

Effect on local conditions

Winds:

Wind is southwesterly, backing south, force 7 Bft. Later in the evening and Thursday night winds back to southeast and will abate to 6 Bft.

Seas: Wave height around 15 ft. Waves will come from westerly directions at first, but from around noon this shifts counter clockwise to a predominantly southwesterly direction. From the afternoon wave height will gradually start to diminish and will be around 7 ft on Thursday morning. Waves still will mostly come from a southerly direction on that day. From Wednesday afternoon till Friday morning there is a risk of westerly swells of 3-5 ft. The combination of dangerous storm surge and large breaking waves will rise water levels by as much as 3-6 ft above normal tide levels.

Rainfall:

Until Thursday thundery showers. Average expected rain amounts 2 inches, with small (20-30%) probabilities for up to 5 inches.

Local authorities and residents of Saba and St. Eustatius are advised to continue monitoring the further progress of this weather system and to take all necessary measures to safeguard life and property.

Center’s latest and forecast positions:

Wed Sep 06 11:00 lt 18.2N 64.0W   108 km   (67 miles) west-north west of Saba.
Wed Sep 06 20:00 lt 19.0N 66.2W   353 km (219 miles) west of Saba.
Moving further away from the islands.

Definitions:

TROPICAL CYCLONE WATCH: A warning for tropical cyclone conditions, including possible sustained winds within the range >= 118 km/h (>=74 mph) (>= 64 knots) are expected in specified areas in 48 hours or less.

Next bulletin: Wednesday September 06, 2017, 15:46 local time

Voor meer informatie, ga naar http://knmidc.org .

 

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Further reading:

The wind speeds indicated above are predictions for sea level conditions. In fact, wind speeds increase with altitude. This is a major challenge for Saba where most dwellings are significantly above sea level.

Click here for a presentation on the observed increase of wind speed with altitude in hurricane conditions.

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