Hurricane Norma Discussion Number 5
NWS National Hurricane Center Miami FL EP172023
300 PM MDT Wed Oct 18 2023
Norma continues to rapidly intensify this afternoon. Intense
inner-core convection has resulted in a ring of very cold cloud tops
surrounding the center of the cyclone, and a ragged eye has emerged
in recent visible images of Norma. The latest subjective Dvorak
classifications from TAFB and SAB were T4.5/77 kt and T4.0/65 kt,
respectively, and the UW-CIMSS objective ADT and AiDT estimates are
around 70 kt. The initial intensity is raised to 70 kt based on a
blend of these data, which makes Norma a hurricane.
Norma has rapidly strengthened by 30 kt during the past 24 h. The
warm waters, weak to moderate vertical shear, and moist and unstable
environment around Norma appear favorable for more steady to rapid
strengthening through early Thursday. The NHC forecast closely
follows the regional hurricane models in the near term and shows
Norma becoming a major hurricane on Thursday. Thereafter, an
increase in southwesterly shear should begin to disrupt the vertical
structure of Norma and cause some weakening on Friday and through
the weekend. The NHC forecast lies on the higher end of the
guidance, closest to HCCA, during the latter part of the period.
Recent microwave and scatterometer fixes indicate that Norma is
moving northward (350/7 kt). A northward to north-northwestward
motion is expected for the next couple of days or so while the storm
moves around a weak ridge to its east. The track models are in good
agreement on this part of the forecast, and the updated NHC track
forecast is faster than the previous one through 72 h, following the
latest HCCA aid. There remains a significant spread in the track
guidance at days 3-5. The GFS and regional hurricane models (HAFS,
HWRF, HMON) show a northward motion near the southern tip of Baja
this weekend, followed by a northeastward motion toward the coast of
western Mexico. Other global models (ECMWF, UKMET, Canadian) show a
shallower Norma stalling or meandering to the southwest of Baja. The
vertical depth and structure of Norma will likely play a major role
in its long-term track, and there is above average uncertainty in
this part of the track forecast. For now, the NHC forecast remains
closer to the stronger GFS-based guidance, although not as fast as
the deterministic GFS solution.
Given the uncertainty described above, it is difficult to pinpoint
the extent or magnitude of potential impacts to portions of Baja
California or western Mexico over the weekend. Interests in these
areas should closely monitor the latest forecast updates, as more
significant track or intensity adjustments could be required in
future advisories.
Key Messages:
1. Norma is forecast to continue rapidly strengthening through
Thursday while it passes well offshore of southwestern Mexico.
2. There remains greater than normal uncertainty in the track and
intensity forecasts for Norma later this week and this weekend while
it approaches the Baja California peninsula and western Mexico.
Regardless, there is an increasing threat of wind and rainfall
impacts to southern portions of Baja California Sur by Saturday,
and watches could be required there tonight or on Thursday.
FORECAST POSITIONS AND MAX WINDS
INIT 18/2100Z 15.6N 108.0W 70 KT 80 MPH
12H 19/0600Z 16.6N 108.1W 85 KT 100 MPH
24H 19/1800Z 17.7N 108.3W 100 KT 115 MPH
36H 20/0600Z 18.7N 108.7W 95 KT 110 MPH
48H 20/1800Z 19.6N 109.1W 85 KT 100 MPH
60H 21/0600Z 20.8N 109.7W 75 KT 85 MPH
72H 21/1800Z 22.1N 110.0W 70 KT 80 MPH
96H 22/1800Z 22.7N 109.9W 65 KT 75 MPH
120H 23/1800Z 24.0N 109.0W 50 KT 60 MPH
$$
Forecaster Reinhart
NWS National Hurricane Center Miami FL EP172023
300 PM MDT Wed Oct 18 2023
Norma continues to rapidly intensify this afternoon. Intense
inner-core convection has resulted in a ring of very cold cloud tops
surrounding the center of the cyclone, and a ragged eye has emerged
in recent visible images of Norma. The latest subjective Dvorak
classifications from TAFB and SAB were T4.5/77 kt and T4.0/65 kt,
respectively, and the UW-CIMSS objective ADT and AiDT estimates are
around 70 kt. The initial intensity is raised to 70 kt based on a
blend of these data, which makes Norma a hurricane.
Norma has rapidly strengthened by 30 kt during the past 24 h. The
warm waters, weak to moderate vertical shear, and moist and unstable
environment around Norma appear favorable for more steady to rapid
strengthening through early Thursday. The NHC forecast closely
follows the regional hurricane models in the near term and shows
Norma becoming a major hurricane on Thursday. Thereafter, an
increase in southwesterly shear should begin to disrupt the vertical
structure of Norma and cause some weakening on Friday and through
the weekend. The NHC forecast lies on the higher end of the
guidance, closest to HCCA, during the latter part of the period.
Recent microwave and scatterometer fixes indicate that Norma is
moving northward (350/7 kt). A northward to north-northwestward
motion is expected for the next couple of days or so while the storm
moves around a weak ridge to its east. The track models are in good
agreement on this part of the forecast, and the updated NHC track
forecast is faster than the previous one through 72 h, following the
latest HCCA aid. There remains a significant spread in the track
guidance at days 3-5. The GFS and regional hurricane models (HAFS,
HWRF, HMON) show a northward motion near the southern tip of Baja
this weekend, followed by a northeastward motion toward the coast of
western Mexico. Other global models (ECMWF, UKMET, Canadian) show a
shallower Norma stalling or meandering to the southwest of Baja. The
vertical depth and structure of Norma will likely play a major role
in its long-term track, and there is above average uncertainty in
this part of the track forecast. For now, the NHC forecast remains
closer to the stronger GFS-based guidance, although not as fast as
the deterministic GFS solution.
Given the uncertainty described above, it is difficult to pinpoint
the extent or magnitude of potential impacts to portions of Baja
California or western Mexico over the weekend. Interests in these
areas should closely monitor the latest forecast updates, as more
significant track or intensity adjustments could be required in
future advisories.
Key Messages:
1. Norma is forecast to continue rapidly strengthening through
Thursday while it passes well offshore of southwestern Mexico.
2. There remains greater than normal uncertainty in the track and
intensity forecasts for Norma later this week and this weekend while
it approaches the Baja California peninsula and western Mexico.
Regardless, there is an increasing threat of wind and rainfall
impacts to southern portions of Baja California Sur by Saturday,
and watches could be required there tonight or on Thursday.
FORECAST POSITIONS AND MAX WINDS
INIT 18/2100Z 15.6N 108.0W 70 KT 80 MPH
12H 19/0600Z 16.6N 108.1W 85 KT 100 MPH
24H 19/1800Z 17.7N 108.3W 100 KT 115 MPH
36H 20/0600Z 18.7N 108.7W 95 KT 110 MPH
48H 20/1800Z 19.6N 109.1W 85 KT 100 MPH
60H 21/0600Z 20.8N 109.7W 75 KT 85 MPH
72H 21/1800Z 22.1N 110.0W 70 KT 80 MPH
96H 22/1800Z 22.7N 109.9W 65 KT 75 MPH
120H 23/1800Z 24.0N 109.0W 50 KT 60 MPH
$$
Forecaster Reinhart
