2019 Atlantic Hurricane Season

Tropical Storm Imelda Discussion Number 2
NWS National Hurricane Center Miami FL AL112019
400 PM CDT Tue Sep 17 2019

Shortly after the earlier NHC Special Advisory, the cyclone quickly
intensified just before it made landfall near Freeport, Texas
around 1800 UTC. A National Ocean Service observing site near
Freeport, Texas, reported sustained winds of 35 kt with a gust to
41 kt, and a minimum pressure of 1005.6 mb. A Weatherflow station
at Surfside Beach also measured sustained winds of 35 kt with a gust
to 44 kt. The advisory intensity is set at 35 kt based on recent
Doppler velocities within some of the rain bands that are still
offshore.

Imelda joins a list of several systems in the northwestern Gulf of
Mexico that formed and intensified very near the Texas coast. Other
recent examples include Allison in 2001 and Humberto in 2007.
Thankfully, in this case Imelda made landfall before significant
strengthening could occur. Now that the center is moving inland,
gradual weakening is expected. It cannot be stressed enough,
however, that the primary threat from Imelda remains very heavy
rainfall and life-threatening flash flooding that will spread
northward into eastern Texas and portions of western Louisiana
during the next day or so.

Imelda is moving northward at about 6 kt. The cyclone should
continue to move slowly northward to north-northwestward around the
western side of a mid-level ridge over the Tennessee Valley until
dissipation occurs in a couple of days. The updated NHC track
forecast has been nudged eastward but remains near the center of the
tightly clustered track guidance.

Key Messages:

1. This system is likely to produce life-threatening flash flooding
along portions of the Upper Texas Coast, including the Houston and
Galveston areas.

500 PM AST Wed Sep 18 2019

Normal communications with the Bermuda Weather Service have been
disrupted due to a lightning strike.

Humberto is taking on more of a hybrid-extratropical structure based
on most of the rain shield having been displaced to the left or
poleward side of the circulation now as seen in Bermuda weather
radar data, and also in conventional and passive microwave satellite
imagery. Sustained hurricane-force winds and gusts have been
measured by amateur radio operators across the island, with a peak
gust to 104 mph having been reported thus far at Ports Island,
Bermuda. The initial intensity of 105 kt on the previous advisory
has been maintained since little overall change in the structure has
occurred since the last aircraft reconnaissance mission 6 hours ago.

The initial motion estimate is 060/17 kt. There are no significant
changes to the previous forecast track or reasoning. Humberto has
basically remained on track during the past 24 hours. The hurricane
is expected to continue accelerating toward the east-northeast
tonight and Thursday morning, with the center expected to pass
about 80 nmi northwest of Bermuda early this evening. A turn toward
the northeast and north-northeast is forecast to occur by early
Thursday afternoon, followed by a motion toward the east-northeast
by 48 hours, with the latter motion continuing through 96 hours. The
new official track forecast is similar to the previous advisory
track, and lies close to the tightly packed TVCN, NOAA-HCCA, and
FSSE consensus track models.

Humberto is now fully embedded within an anticyclonically curved
right-rear jet entrance region. As a result, some fluctuations in
strength could occur during the next 12 hours or so. Thereafter,
strong southwesterly vertical wind shear in excess of 50 kt, along
with cold upwelling beneath the hurricane, should combine to induce
steady weakening. By 48 hours, the global models continue to
forecast Humberto to merge with a frontal system, and the NHC
intensity forecast calls for extratropical transition around that
time. The official intensity forecast follows an average of the
global models' intensity forecasts due to Humberto's hybrid nature,
which is not being captured properly by the tropical-cyclone-based
consensus intensity models.

Key Messages:

1. A prolonged period of dangerous winds is expected to continue on
Bermuda through Thursday morning, with hurricane-force winds
expected during the next several hours. Preparations to protect
life and property should be rushed to completion.

2. Storm surge and dangerous breaking waves could cause coastal
flooding tonight and Thursday along the southern coast of Bermuda.

3. Swells will continue to affect the northwestern Bahamas and the
southeastern coast of the United States from east-central Florida to
North Carolina during the next couple of days, creating life-
threatening surf and rip current conditions.

FORECAST POSITIONS AND MAX WINDS

INIT 18/2100Z 33.0N 66.3W 105 KT 120 MPH
12H 19/0600Z 34.6N 63.6W 105 KT 120 MPH
24H 19/1800Z 37.4N 61.0W 95 KT 110 MPH
36H 20/0600Z 39.8N 60.0W 75 KT 85 MPH
48H 20/1800Z 41.6N 58.7W 60 KT 70 MPH...POST-TROP/EXTRATROP
72H 21/1800Z 43.9N 47.0W 45 KT 50 MPH...POST-TROP/EXTRATROP
96H 22/1800Z 49.0N 30.0W 45 KT 50 MPH...POST-TROP/EXTRATROP
120H 23/1800Z...DISSIPATED/ABSORBED

1100 PM AST Thu Sep 19 2019

The Air Force Hurricane Hunters investigating Jerry this evening found that the hurricane has strengthened. Based on the 700 mb flight-level winds from the aircraft, the current intensity is estimated to be about 90 kt. It should be noted that this is substantially higher than the intensity estimates provided from satellite data, and underscores the value of aerial reconnaissance of tropical cyclones. An expected increase in vertical shear in a day or so is expected to cause a weakening trend to commence in 12 to 24 hours, however, Jerry should remain a hurricane throughout the forecast period. This NHC intensity forecast is higher than the previous one mainly due to the higher initial wind speed, and is near or a little above the model consensus.

Graces7 wrote: »

Any time frame for Humberto please?