Tropical Storm Bonnie Discussion Number 22...Retransmitted
NWS National Hurricane Center Miami FL EP042022
1000 PM CDT Sat Jul 02 2022
This evening's conventional satellite presentation consists of an
impressive deep convective curved band with -83C cloud tops
encompassing the west side of the cyclone. Earlier SSM/S and AMSR2
microwave passes revealed inner core ring development that was about
60 percent closed in the northern quadrants. There appears to be a
slight vertical tilt toward the west, more than likely due to the
period it spent moving across Nicaragua. The initial intensity is
raised to 50 kt and is based on a compromise of the various
subjective and objective satellite intensity estimates.
The shear is low, the water is warm, and the atmosphere is moist,
all contributing to further strengthening during the next few days,
and Bonnie is expected to become a hurricane in 24 hours. Around
mid-period, the global models and the GFS/ECMWF SHIPS intensity
guidance show modest northeasterly shear impinging on Bonnie's
outflow pattern. As a result, the official intensity forecast
calls for a slight weakening beyond day 3.
Bonnie's initial motion is estimated to be due west or 270/15 kt.
A mid-tropospheric ridge stretching from the northern Gulf of
Mexico to the Baja California peninsula should cause the cyclone to
turn west-northwestward Sunday and continue in this heading through
the remainder of the forecast period. The global and regional
model track guidance remains in agreement, and these tightly
clustered aids, as well as the NHC forecast, takes Bonnie
approximately parallel to the coasts and keeps the
tropical-storm-force winds offshore of the southern coast of
Central America and Mexico. However, interests in coastal El
Salvador, Guatemala, and southwestern Mexico should closely monitor
Bonnie's forecast track for the next few days as a slight northward
adjustment to the track could require tropical storm watches for
portions of this coastline.
KEY MESSAGES:
1. Areas of heavy rainfall are expected across portions of
Nicaragua, Costa Rica and the southern portion of El Salvador
through tonight. This rainfall may cause some instances of flash
flooding and mudslides across the region.
2. Interests along the coasts of Honduras, El Salvador, Guatemala,
and southeastern Mexico should monitor the progress of this system.
While the center of Bonnie is forecast to stay offshore, any
northward adjustment in the track forecast could require the
issuance of a tropical storm watch for part of this area.
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.
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