[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 020858
TCDAT2

Tropical Storm Bonnie Discussion Number  19
NWS National Hurricane Center Miami FL       AL022022
400 AM CDT Sat Jul 02 2022

Overall, Bonnie's structure is holding together quite well as the
storm moves across Central America. While the coldest cloud tops
near the center have warmed somewhat, radar from the Nicaraguan
Weather Service in Las Nubes shows a healthy reflectivity structure.
In fact, after the last center fix the Air Force Reserve Hurricane
Hunter aircraft made indicated a formative eyewall was developing
with Bonnie, a similar signature is now also currently observed with
Bonnie over Lake Nicaragua. Assuming there has been some weakening
of the wind field since Bonnie began moving over land, the
intensity is being reduced to an uncertain 35 kt for this advisory.

Bonnie was moving just north of due west from the recon fixes last
night, and the initial motion has been maintained at 275/14 kt. A
strong deep-layer ridge poleward of Bonnie should continue to steer
the cyclone west to west-northwestward for the majority of the
forecast period after it moves offshore. This track continues to
take Bonnie roughly parallel to the southern coast of Central
America and Mexico. The track guidance remains in good agreement
this cycle, and only slight changes to the forecast track were made,
mostly a somewhat faster motion at the end of the forecast period.
While the relatively small size of the tropical cyclone is currently
forecast to keep the highest winds offshore, interests in coastal El
Salvador, Guatemala, and southwestern Mexico should continue to
monitor Bonnie's track for the next few days, as any northward track
adjustments could require tropical storm watches for portions of
this coastline.

So far Bonnie's structure does not appear to be that adversely
affected by its ongoing land interaction crossing Central America,
perhaps because it is traversing a relatively flat gap across Lake
Nicaragua, in between higher terrain to its north or south. However,
one thorn in the system's short-term intensity forecast is that sea
surface temperatures (SSTs) just offshore Nicaragua are not all that
warm, only between 26-27 C with a very shallow depth of these
marginally warm waters for the first 24 h or so. For this reason,
only slow intensification is forecasted early on, which is under the
majority of the guidance in this time frame. Afterwards, SSTs
markedly warm to above 28 C, and vertical wind shear is expected to
remain only light to moderate. Thus, a faster rate of
intensification is anticipated after 36 h, and Bonnie is still
forecast to become a hurricane in about three days. The latest
intensity forecast has been adjusted downward in the short-term, but
still peaks the storm as a 75-kt hurricane at the end of the
forecast period.

It is worth mentioning that Bonnie's low-level circulation is
expected to survive its passage across Central America, similar to
that of Hurricane Otto back in 2016. Thus, the system is expected to
retain its name even after it moves into the far eastern Pacific
later today.  The intermediate advisory at 1200 UTC will be issued
under the same Atlantic header as before.  Product headers will
change to eastern Pacific headers beginning with the next complete
advisory at 1500 UTC, with the ATCF identifier changing from
AL022022 to EP042022.


KEY MESSAGES:

1. Heavy rainfall is expected across portions of Nicaragua and
Costa Rica today. Life-threatening flash flooding and mudslides are
expected.

2. Tropical storm conditions are expected along the Caribbean
coasts of Costa Rica and Nicaragua within the Tropical Storm Warning
areas for the next several hours, and along the Pacific coasts of
Costa Rica and Nicaragua today.


FORECAST POSITIONS AND MAX WINDS

INIT  02/0900Z 11.3N  85.1W   35 KT  40 MPH...OVER LAKE NICARAGUA
 12H  02/1800Z 11.3N  87.1W   35 KT  40 MPH...OVER PACIFIC OCEAN
 24H  03/0600Z 11.5N  89.4W   40 KT  45 MPH
 36H  03/1800Z 12.0N  91.9W   45 KT  50 MPH
 48H  04/0600Z 13.0N  95.0W   55 KT  65 MPH
 60H  04/1800Z 13.9N  98.0W   60 KT  70 MPH
 72H  05/0600Z 14.7N 101.0W   65 KT  75 MPH
 96H  06/0600Z 16.0N 106.4W   75 KT  85 MPH
120H  07/0600Z 16.4N 110.5W   75 KT  85 MPH

$$
Forecaster Papin
This weather bulletin was brought to you by:
www.nashvilleweather.net