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.

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

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).

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).

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:

https://twitter.com/pppapin/status/889949617315557377

Between reviews and revisions and writing and analysis and service and advising and recording and constant constant adjusting, I'm expecting to average 70 hours of work a week this summer.

By the way, only one of my three summer months comes with salary. And that's a grant. I can't remember the last time I took more than a weekend off work. And all this piles on top of the ongoing uncertainty surrounding the pandemic, our economy, our society, our politics, & the future of higher ed.

I'm burned out. And I'm not sure how to find time to recuperate.

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)

In addition to radar, we can also monitor today's severe weather from space. Here's 4 hours of 1-minute mesoscale Sandwich RGB (left) and Day Cloud Phase RGB (right) imagery from the NOAA GOES Image Viewer. These and more products are available here: star.nesdis.noaa.gov/GOES/meso.php?… Quick guide to Sandwich RGB (2-page PDF): star.nesdis.noaa.gov/GOES/documents…

Quick guide to Day Cloud Phase RGB (2-page PDF): star.nesdis.noaa.gov/GOES/documents…

48 hours of Cyclone Harold using 10-minute AHI imagery from Himawari-8, now a Category 4-equivalent storm bearing down on Vanuatu. Displayed maximum wind speeds are produced in real time by the CIMSS Advanced Dvorak Technique (ADT): tropic.ssec.wisc.edu/real-time/adt/… Cyclone Harold made landfall in Vanuatu a couple of hours ago still packing Category 4 strength winds. Here's a zoomed-in image of the cyclone's eye reaching the Vanuatu coast near 2300 UTC 5 April. For scale, the dashed circle shows a 200-km distance from the estimated center.

This GOES RGB product helps us monitor convective development during the day because the colors change as cumulus clouds become cumulonimbus clouds (because the clouds are developing more ice particles).

https://twitter.com/bill_line/status/1243994522821918721

It combines Band 2 (the 0.5-km "red" band), Band 5 (the "snow/ice" band), and Band 13 ("clean longwave infrared"). Bands 2 and 5 detect reflected sunlight and are thus daytime-only bands.

How does this product work? 1) Water clouds reflect light differently than ice clouds!

You don't need another coronavirus-related tweet thread in your feed... but I want to track the cases in Mississippi according to the MS Department of Health. We're now at 377 cases and 3 deaths, up from 320 cases and 1 death yesterday. Source: msdh.ms.gov/msdhsite/_stat… Big spike in Mississippi coronavirus numbers... yet the map still shows yesterday's date.

This implies we're finally starting to get numbers that reflect the reality of spread in this state.

Teaching friends, have you created resources you're willing to share or crafted a stash of links to existing tools that would help our future meteorologists tackle dynamics or phys met in a new learning environment?

I'm happy to host a landing page with these links if it'd help.

https://twitter.com/TylerJRoney/status/1238249034361573377

The first two tools that came to my mind were MetEd's interactive widgets for the QG omega and vorticity equations, but I know more must be out there.

QG omega: meted.ucar.edu/bom/qgoe/
QG vorticity: meted.ucar.edu/dynamics/qgve/

Even in January, most Northern Hemisphere sea surface temperatures (SSTs) are increasing.

This map shows the difference between the 1991-2020 average and the 1981-2010 average for January according to JMA's monthly COBE SST dataset. Source data: ds.data.jma.go.jp/tcc/tcc/produc… From the same dataset as above, long-term average SSTs in February are generally increasing too. Multiple "hotspots" include the Sea of Japan and the Atlantic near Maine and Nova Scotia.

Hello snow View from the ground

It feels like 2019 North Atlantic tropical cyclones (TCs) have been moving slower *and* closer to land compared to normal. So I investigated.

Yes, 2019 TCs have generally been closer to land (left image) + often moved slower (right image) vs 1989-2018. More details in thread: To be included in this analysis, TCs had to be tropical or subtropical with maximum sustained winds of at least 34 knots. Distance from land was calculated as nearest elevation >= 1 meter (to better catch islands) using 2-minute gridded global relief data: ngdc.noaa.gov/mgg/global/eto…

Yesterday morning, we picked up our cat Tomo from his regular vet where he'd been boarded while we were gone. They said he did fine. Fast forward to now: we're at the emergency vet because he hasn't been doing well today. Thoughts/prayers appreciated. We're a bit emotional because the last time we were here was two years ago when we had to put my cat Raven to sleep after he lost his battle with cancer.