Issued at 400 PM CDT Fri Sep 18 2020
000
WTNT42 KNHC 182053
TCDAT2
Tropical Storm Beta Discussion Number 5
NWS National Hurricane Center Miami FL AL222020
400 PM CDT Fri Sep 18 2020
Satellite imagery indicates that the circulation of Tropical
Depression 22 has become better defined, and most objective and
subjective satellite intensity estimates are now 35 kt. Based on
this, along with 33 kt 1-mi average winds from NOAA buoy 42002, the
depression is upgraded to Tropical Storm Beta with an initial
intensity of 35 kt. Although the system is now a tropical storm,
satellite imagery shows that the convective pattern is becoming
elongated due to the effects of southwesterly vertical wind shear.
Visible imagery and scatterometer data showed that the center of
Beta was a bit farther east than previously thought, and the initial
motion is a somewhat uncertain 025/8. This motion should continue
for the next 12-24 h as the storm is steered by a mid- to
upper-level trough over Texas and northeastern Mexico. After that
time, the trough should weaken and lift out to the northeast, with a
mid-level ridge building to the north of the cyclone above an
already present low-level ridge. This ridge should act as a Beta
blocker, causing the storm to turn westward toward the western Gulf
coast. Between 72-120 h, the mid-level ridge weakens as another
mid-latitude trough moves through the central United States, and
this is expected to cause the storm to slowly recurve toward the
northeast. One change in the track guidance since the previous
forecast is that the GFS and ECMWF are a bit faster on the westward
motion and show the center near the Texas coast in about 72 h. The
latter part of the new track forecast also shifts westward, but it
is still to the east of the GFS/ECMWF. There is also a chance that
Beta could move more northward than forecast before the trough lifts
out, which adds an additional touch of uncertainty to the track
forecast. So, it is critical that users not focus on the exact
forecast track, especially at days 3 to 5.
The global models suggest that the current shear may decrease a
little after 24 h when the upper-level trough moves away from Beta.
However, there is a chance of at least some dry air entrainment
that would hamper strengthening. The intensity guidance for the
most part continues to forecast Beta to reach a peak intensity
below hurricane strength, although the latest SHIPS model forecasts
a peak intensity near 65 kt. The new intensity forecast is again
unchanged in making Beta a hurricane at 60 and 72 h, and it lies at
the upper edge of the intensity guidance.
Key Messages:
1. Beta is expected to strengthen and possibly become a hurricane,
while moving slowly over the western Gulf of Mexico during the next
few days.
2. There is an increasing risk of heavy rainfall and flooding along
the northwest Gulf Coast Sunday through at least the middle of next
week as Beta is forecast to move slowly toward and along or offshore
of the coast through that time. For additional information, see
products from your local National Weather Service office.
3. While it is too early to determine what areas could see direct
wind and storm surge impacts from Beta, interests throughout
the western Gulf of Mexico should monitor the progress of this
system and future updates to the forecast. Storm Surge and
Tropical Storm or Hurricane watches could be issued tonight or
Saturday.
FORECAST POSITIONS AND MAX WINDS
INIT 18/2100Z 24.3N 93.1W 35 KT 40 MPH
12H 19/0600Z 25.1N 92.9W 40 KT 45 MPH
24H 19/1800Z 25.9N 93.0W 45 KT 50 MPH
36H 20/0600Z 26.1N 93.7W 50 KT 60 MPH
48H 20/1800Z 26.3N 94.6W 60 KT 70 MPH
60H 21/0600Z 26.5N 95.5W 65 KT 75 MPH
72H 21/1800Z 26.8N 96.3W 65 KT 75 MPH
96H 22/1800Z 27.5N 96.5W 60 KT 70 MPH
120H 23/1800Z 28.5N 96.0W 55 KT 65 MPH
$$
Forecaster Beven
Continue reading...
000
WTNT42 KNHC 182053
TCDAT2
Tropical Storm Beta Discussion Number 5
NWS National Hurricane Center Miami FL AL222020
400 PM CDT Fri Sep 18 2020
Satellite imagery indicates that the circulation of Tropical
Depression 22 has become better defined, and most objective and
subjective satellite intensity estimates are now 35 kt. Based on
this, along with 33 kt 1-mi average winds from NOAA buoy 42002, the
depression is upgraded to Tropical Storm Beta with an initial
intensity of 35 kt. Although the system is now a tropical storm,
satellite imagery shows that the convective pattern is becoming
elongated due to the effects of southwesterly vertical wind shear.
Visible imagery and scatterometer data showed that the center of
Beta was a bit farther east than previously thought, and the initial
motion is a somewhat uncertain 025/8. This motion should continue
for the next 12-24 h as the storm is steered by a mid- to
upper-level trough over Texas and northeastern Mexico. After that
time, the trough should weaken and lift out to the northeast, with a
mid-level ridge building to the north of the cyclone above an
already present low-level ridge. This ridge should act as a Beta
blocker, causing the storm to turn westward toward the western Gulf
coast. Between 72-120 h, the mid-level ridge weakens as another
mid-latitude trough moves through the central United States, and
this is expected to cause the storm to slowly recurve toward the
northeast. One change in the track guidance since the previous
forecast is that the GFS and ECMWF are a bit faster on the westward
motion and show the center near the Texas coast in about 72 h. The
latter part of the new track forecast also shifts westward, but it
is still to the east of the GFS/ECMWF. There is also a chance that
Beta could move more northward than forecast before the trough lifts
out, which adds an additional touch of uncertainty to the track
forecast. So, it is critical that users not focus on the exact
forecast track, especially at days 3 to 5.
The global models suggest that the current shear may decrease a
little after 24 h when the upper-level trough moves away from Beta.
However, there is a chance of at least some dry air entrainment
that would hamper strengthening. The intensity guidance for the
most part continues to forecast Beta to reach a peak intensity
below hurricane strength, although the latest SHIPS model forecasts
a peak intensity near 65 kt. The new intensity forecast is again
unchanged in making Beta a hurricane at 60 and 72 h, and it lies at
the upper edge of the intensity guidance.
Key Messages:
1. Beta is expected to strengthen and possibly become a hurricane,
while moving slowly over the western Gulf of Mexico during the next
few days.
2. There is an increasing risk of heavy rainfall and flooding along
the northwest Gulf Coast Sunday through at least the middle of next
week as Beta is forecast to move slowly toward and along or offshore
of the coast through that time. For additional information, see
products from your local National Weather Service office.
3. While it is too early to determine what areas could see direct
wind and storm surge impacts from Beta, interests throughout
the western Gulf of Mexico should monitor the progress of this
system and future updates to the forecast. Storm Surge and
Tropical Storm or Hurricane watches could be issued tonight or
Saturday.
FORECAST POSITIONS AND MAX WINDS
INIT 18/2100Z 24.3N 93.1W 35 KT 40 MPH
12H 19/0600Z 25.1N 92.9W 40 KT 45 MPH
24H 19/1800Z 25.9N 93.0W 45 KT 50 MPH
36H 20/0600Z 26.1N 93.7W 50 KT 60 MPH
48H 20/1800Z 26.3N 94.6W 60 KT 70 MPH
60H 21/0600Z 26.5N 95.5W 65 KT 75 MPH
72H 21/1800Z 26.8N 96.3W 65 KT 75 MPH
96H 22/1800Z 27.5N 96.5W 60 KT 70 MPH
120H 23/1800Z 28.5N 96.0W 55 KT 65 MPH
$$
Forecaster Beven
Continue reading...