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Tropical Storm Nana Discussion Number 3
NWS National Hurricane Center Miami FL AL162020
500 PM EDT Tue Sep 01 2020
Although convection has waned somewhat since the previous advisory
due to mid-level dry air entrainment, Nana still has enough deep
convection over and surrounding the low-level center to keep the
intensity at 45 kt. Upper-level outflow has continued to improve,
with the associated anticyclone becoming more symmetrical. Another
reconnaissance mission is scheduled for this evening.
The initial motion estimate is 275/16 kt. There are no significant
changes to the previous track forecast or reasoning. A pronounced
deep-layer to the north of Nana is forecast to remain intact and
even build westward over the next few days, keeping Nana moving in a
general westward direction for the next 36 hours or so. Thereafter,
the aforementioned ridge is expected to build west-southwestward
across southern Mexico, driving the cyclone west-southwestward as
well across northern Central America. The new NHC forecast track is
similar to the previous advisory track, and lies close to a blend of
the simple consensus models TVCN and GFEX, and the corrected-
consensus models NOAA-HCCA and FSSE.
The current northeasterly 15 kt of vertical wind shear and dry air
intrusions should inhibit development for next 24 hours or so.
However, the GFS and ECMWF models both forecast the shear to
gradually decrease during the next 48 hours, becoming near 5 kt by
36 hours. The lower vertical shear, coupled with the already
impressive outflow pattern, sea-surface temperatures of 29.5-30.5
deg C, and a moistening mid-level environment should allow for
gradual strengthening for the next 24 hours, followed by more
significant intensification thereafter, which will continue right up
until landfall occurs. The NHC official intensity forecast is a
blend of the simple consensus intensity model IVCN, and the
corrected-consensus models NOAA-HCCA and FSSE.
A Tropical Storm Warning and Tropical Storm Watch have been issued
for the southern portion of the Yucatan Peninsula and the
Caribbean Sea coast of Guatemala, respectively.
1. Tropical Storm Nana is now forecast to be a hurricane as it
approaches the coast, and interests in Honduras, Guatemala,
Belize, and Yucatan should closely monitor the progress of this
storm. Strong winds, dangerous storm surge and very heavy rainfall
causing flash flooding are becoming more likely from Nana.
FORECAST POSITIONS AND MAX WINDS
INIT 01/2100Z 16.8N 79.3W 45 KT 50 MPH
12H 02/0600Z 17.1N 81.5W 50 KT 60 MPH
24H 02/1800Z 17.3N 84.7W 55 KT 65 MPH
36H 03/0600Z 17.2N 87.3W 65 KT 75 MPH
48H 03/1800Z 16.9N 89.4W 45 KT 50 MPH...INLAND
60H 04/0600Z 16.5N 91.7W 20 KT 25 MPH...POST-TROP/REMNT LOW