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Dr. Kim Wood Profile picture
@DrKimWood
Apr 23, 2020 • 4 tweets • 3 min read • Read on X
Hello Invest #90E. In *checks notes* ...April.

There are no tropical cyclones of any intensity in the eastern North Pacific best-track record (1966-2019) during the month of April. If this disturbance becomes a tropical depression in the next few days, it'll be the first.
The atmosphere and ocean seem relatively conducive for development: SSTs > 26.5C, lots of moisture, increased low-level (850-hPa) vorticity. Vertical wind shear increases to its north, though.

(Below images except the SST map were provided by CIMSS: tropic.ssec.wisc.edu) ImageImageImageImage
The NHC gives this disturbance a 40% chance of development in the next 5 days:
The NHC's outlook has increased to an 80% chance of development. #90E's satellite presentation continues to improve today, and the environment has been conducive in part due to the passage of a Kelvin wave as noted by @pppapin

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More from @DrKimWood

Dr. Kim Wood Profile picture
Aug 16
With respect to tropical cyclone count, 2024 may feel "slow" at this time given high seasonal forecasts.

But when we use an index like Accumulated Cyclone Energy, which incorporates a storm's intensity + duration, 2024 resembles 2020.

The season higher than 2024 so far is 2005. Image
Also, we haven't yet reached the peak of the season. September is, on average, the most active month in the Atlantic. For example, 10 TCs occurred in September 2020.

On the above chart, the thin gray lines each represent one year from 1988-2023.
A season can have periods of less activity or inactivity due to factors such as equatorial waves or the Madden-Julian oscillation, which -- depending on location and strength -- can increase sinking air and/or vertical wind shear over the Atlantic basin, which limit TC activity. Image
Read 5 tweets
Dr. Kim Wood Profile picture
Aug 17, 2023
Okay, let's get complicated for a moment. 🧵

On the downwind (leeward) side of mountains, air likes to spin more. That is, we observe increased vorticity. The amount and location (distribution) of low-level vorticity can affect TC behavior, like where and how fast it moves.
In the Northern Hemisphere, a TC's winds "spin" counterclockwise. Hilary is already a large TC, so those winds extend far from its center. Since Hilary is expected to move parallel the Mexican coast, winds on its eastern side may extend over the mountains of western Mexico.
That possibility could lead to somewhat enhanced low-level vorticity as those winds *from the TC circulation itself* descend down the Baja California mountains back toward the ocean.
Read 8 tweets
Dr. Kim Wood Profile picture
Sep 23, 2020
According to the NHC's archive, since 1966 -- the start of the satellite era -- there have been 21 "zombie" named storms that reached an intensity of ≥34 kt as a tropical/subtropical storm, then became a remnant low or extratropical, and later regained tropical characteristics:
1981 Dennis, 3 days
1998 Mitch, 2 days
2001 Dean, 3.25 days
2001 Erin, 1.25 days
2002 Lili, 1.75 days
2004 Ivan, 4.25 days
2005 Gamma, 2.25 days
2009 Ana, 2 days
2010 Colin, 2 days
2011 Emily, 2.25 days
2011 Maria, 1.25 days
2011 Ophelia, 2.25 days
2012 Nadine, 1.5 days
2013 Dorian, 6.25 days
2013 Humberto, 1.25 days
2016 Bonnie, 2.75 days
2017 Harvey, 4 days
2017 Lee, 2.25 days
2018 Beryl, 6.25 days
2018 Kirk, 2.75 days
2018 Leslie, 3.25 days
Read 5 tweets
Dr. Kim Wood Profile picture
Sep 18, 2020
The "Nth" named storm records that the 2020 Atlantic hurricane season has broken so far: a thread
Cristobal: 3rd earliest named storm at 12 UTC on 2 June, defeating 2016 Colin's record of 18 UTC on 5 June (3.25 days).
Edouard: 5th earliest named storm at 00 UTC on 6 July, defeating 2005 Emily's record of 00 UTC on 12 July (6.0 days).
Read 21 tweets
Dr. Kim Wood Profile picture
Aug 29, 2020
Some perspective on the location of Laura's strongest winds (and common criteria those winds "translate" to):

- Tropical storm-force winds = gale-force winds
- 50+ kt = threshold for NWS severe t-storm warning
- 64+ kt = hurricane force
- 100+ kt = the RARE extreme wind warning
The winds associated with Laura's category 4 designation are confined to a TINY area near the storm center. Yet strong winds were widespread and extended FAR from the center, especially on the right side (where surge was worst because the large wind field pointed AT the coast).
Many, many folks have been affected by Laura's impacts and continue to wrestle with the aftermath. Widespread devastation extends the length of recovery, too.

But note that far fewer -- thankfully -- would've felt those "category 4" winds.
Read 7 tweets
Dr. Kim Wood Profile picture
Aug 21, 2020
A short thread of real-world examples of the Fujiwhara effect (tropical cyclones can interact when their centers move within ~900 miles of each other, meaning they affect each other's movement and may even merge).

1) Wilma vs Alpha in 2005 -- Wilma absorbs the weaker Alpha
2) Hilary vs Irwin in the eastern North Pacific in 2017 -- the two storms swirl around each other until Hilary falls apart (3-hour resolution imagery)

Also see the excellent explainer by @pppapin:
3) Iris vs Karen in 1995 -- as they dance, Iris jogs eastward and Karen accelerates northward around Iris.

Oh, Luis and Humberto are in here too. 1995 was ridiculous until 2005 came along. (It was also the season that got me into hurricanes.)
Read 5 tweets

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