Tropical Storm #Helene Advisory 3: Tropical Storm Helene Forms Between the Coast of Africa and the Cabo Verde Islands


Tropical Storm Helene Advisory Number   3
NWS National Hurricane Center Miami FL       AL082018
1100 PM AST Fri Sep 07 2018

...TROPICAL STORM HELENE FORMS BETWEEN THE COAST OF AFRICA AND THE
CABO VERDE ISLANDS...
...EXPECTED TO BRING TROPICAL STORM CONDITIONS TO PORTIONS OF THE
CABO VERDE ISLANDS SATURDAY NIGHT AND SUNDAY.


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...13.6N 18.5W
ABOUT 405 MI...650 KM E OF THE SOUTHERNMOST CABO VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...1002 MB...29.59 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:

None.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Tropical Storm Warning is in effect for...
* Santiago, Fogo, and Brava

A Tropical Storm Warning means that tropical storm conditions are
expected somewhere within the warning area within 36 hours.

For storm information specific to your area, please monitor products
issued by your national meteorological service.


DISCUSSION AND OUTLOOK
----------------------
Satellite data indicate that the depression over the far eastern
Atlantic has strengthened and is now Tropical Storm Helene. The
center of the tropical storm is a little to the east of
previously indicated position, and at 1100 PM AST (0300 UTC) was
located near latitude 13.6 North, longitude 18.5 West. Helene is
moving toward the west near 12 mph (19 km/h), and a westward to
west-northwestward motion with a gradual increase in forward speed
is expected during the next 72 hours.  On this track, Helene will be
passing very close to the southern Cabo Verde Islands during
Saturday night and early Sunday.

Maximum sustained winds are near 40 mph (65 km/h) with higher gusts.
Some strengthening is forecast during the next 2 to 3 days, and
Helene could become a hurricane early next week.

Tropical-storm-force winds extend outward up to 70 miles (110 km).
mainly to the south of the center.

The estimated minimum central pressure is 1002 mb (29.59 inches).


HAZARDS AFFECTING LAND
----------------------
WIND:  Tropical storm conditions are expected to first reach the
warning area Saturday night or on Sunday.

RAINFALL:  Helene is expected to produce total rain accumulations of
3 to 5 inches, with maximum totals of 8 inches across the southern
Cabo Verde Islands.  This rainfall may produce life-threatening
flash floods.
Tropical Storm Helene Discussion Number   3
NWS National Hurricane Center Miami FL       AL082018
1100 PM AST Fri Sep 07 2018

A very timely ASCAT pass indicated that the winds associated with
the depression have increased to 35 kt, and also that the center was
a little east of the location previously indicated. This is very
common in systems during the formative stage.  Based on the ASCAT
data, the system has been upgraded to Tropical Storm Helene, the
eighth named storm of the season. The satellite presentation has
also improved during the past several hours, and now the cyclone has
large cyclonically curved convective bands to the south of the
center. The outflow is fair in all quadrants.

Helene will be moving over warm waters and within an environment
of light shear through the next 3 to 4 days, and most of the
guidance responds to that environment by gradually strengthening the
cyclone. The NHC forecast follows the trend of the intensity
consensus, and brings Helene to hurricane intensity in about 3 days.

Currently, Helene is embedded within a southwest monsoon-type flow,
and is moving toward the west at about 9 or 10 knots. However, as
the cyclone moves away from the African coast, it will become
steered by the easterly flow around the subtropical ridge and should
then increase in forward speed. Most of the track models are in
extremely good agreement, at least for the next 3 days when the
confidence in the forecast is high. At the long range, a mid-level
trough is expected to develop over the central Atlantic, forcing the
cyclone to turn more to the northwest and even north later on. The
NHC forecast is in the middle of the guidance envelope and basically
on top of the corrected consensus HCCA.


FORECAST POSITIONS AND MAX WINDS

INIT  08/0300Z 13.6N  18.5W   35 KT  40 MPH
 12H  08/1200Z 13.8N  19.9W   35 KT  40 MPH
 24H  09/0000Z 14.3N  22.3W   40 KT  45 MPH
 36H  09/1200Z 14.8N  25.0W   50 KT  60 MPH
 48H  10/0000Z 15.4N  28.0W   55 KT  65 MPH
 72H  11/0000Z 17.0N  33.9W   65 KT  75 MPH
 96H  12/0000Z 18.5N  39.0W   65 KT  75 MPH
120H  13/0000Z 20.5N  42.5W   60 KT  70 MPH



NEXT ADVISORY
-------------
Next intermediate advisory at 200 AM AST.
Next complete advisory at 500 AM AST.
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