After previously reaching Category 4 intensity on 23 February, Super Typhoon Wutip underwent an eyewall replacement cycle (MIMIC-TC) and emerged to reach Category 5 intensity at 06 UTC on 25 February 2019 (ADT | SATCON) — becoming the strongest (and only Category 5) February tropical cyclone on record for the Northwest Pacific basin (and also for the Northern Hemisphere). Rapid scan (2.5-minute) Himawari-8 “Clean” Infrared Window (10.4 µm) images (above) displayed a well-defined eye with an annular to axisymmetric eyewall structure; mesovortices could also be seen circulating within the eye. Of particular interest were the series of gravity waves propagating radially outward from the eye during the first few hours of the animation.

In addition, note the arc of cooling cloud tops south of the eye beginning around 1530 UTC. A comparison of Himawari-8 Infrared and Infrared-Water Vapor brightness temperature difference (BTD) images from the CIMSS Tropical Cyclones site (below) revealed increasing BTD values within that arc of colder clouds — an indication of convective overshooting tops that were likely penetrating into the stratosphere.

Himawari-8 “Red” Visible (0.64 µm) images (below) provided a clearer view of the mesovortices within the eye.

Satellite-derived deep-layer wind shear in the vicinity of Wutip was very light — in the range of 5-10 knots — surrounding the time period when Wutip peaked at Category 5 intensity at 06 UTC (below).

Wutip continued to exhibit a well-defined poleward outflow channel (below), although mid-upper level outflow was good in all quadrants of the storm (which aided the intensification process).

Although Ocean Heat Content was modest, Sea Surface Temperature values around 28ºC were favorable (below).

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Tropical systems over the western Pacific are in a region where surface observations are few and far between.  Imagers on geostationary satellites, such as the Advanced Himawari Imagery (AHI) on Himawari-8, shown above, capably track such systems, but sounders do a much better job diagnosing the atmosphere through and towards which storms are moving.  Data from the Cross-track Infrared Sounder (CrIS) on Suomi NPP (and NOAA-20) is combined with microwave sounder from ATMS (the Advanced Technology Microwave Sounder) also on Suomi NPP (and NOAA-20) to produce NUCAPS (NOAA-Unique Combined Atmospheric Profiling System) Soundings.  These vertical profiles (independent of numerical model simulations) can provide information that is difficult to find elsewhere.  The AHI Clean Window image above is overlain with a swath of NUCAPS Sounding points, and seven (noted on the image as 1-7) are shown below. In the image, NUCAPS profile points coded green denote successful infrared and microwave retrievals; yellow denotes an infrared retrieval that failed, but a microwave retrieval was successful; red denotes failure in both infrared and microwave retrievals — typically meaning that they both failed to converge. Infrared retrievals are most likely to fail in regions of thick clouds, microwave retrievals are most likely to fail in regions of heavy precipitation.

Microwave data alone can also be used to diagnose precipitable water, and an estimate from the MIMIC Total Precipitable Water website for the 24 hours ending at 1400 UTC on 25 February 2019 is shown above.  There is considerable dry air in advance of Wutip, and dry air is also wrapping around the south and east of the storm.

Profile 2 for example, was taken over Guam at 0329 UTC on 25 February 2019 and is shown below. Total Precipitable Water at this time was 1.32″, fairly low for a tropical region. The animation of the Guam radiosondes from 0000 UTC on 24 February to 1200 UTC on 25 February is shown beneath the NUCAPS profile.  Total Precipitable Water values over Guam as determined by the radiosonde exceeded 2.3″ on 24 February before dropping to 1.86″ at 00 UTC on the 25th, and 1.37″ on 1200 UTC on 25 February.  The NUCAPS plot over Guam gives an extra observation point — at 0330 UTC, in between ‘normal’ synoptic times — to confirm the arrival of dry air.

NUCAPS suggests that the dry air south of Wutip is exceptionally dry indeed. The NUCAPS plot from Point 7, above, shown below, shows a total Precipitable water in the deep tropics of only 0.5″!

You can also view other NUCAPS profiles by clicking on the number: 1, 3, 4, 5, 6. Point 4, to the north of Wutip, shows more moisture than the other points. Equilibrium Levels for each of the points north of Wutip are near the tropopause.

Horizontal fields derived from NUCAPS values (for example, Dewpoint temperature at 700 mb) will be available in AWIPS later this year. Himawari imagery in this post courtesy of the Japan Meteorological Agency (JMA).

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GOES-16 viewed the development of a house fire over rural Winnebago County in Nekimi Township, west of Lake Winnebago on late Sunday night 24 February 2019.  The animation above shows warm pixel developing starting at 0439 UTC.  One-minute imagery was available because the county falls within the northern part of the westernmost default mesoscale sector for GOES-16.

The toggle below compares the 0438 and 0439 UTC imagery.  (Actually 04:38:51 and 04:39:51).  The fire becomes apparent to GOES in the later image. Google satellite views suggest the house had a footprint around 2000 square feet.

Winnebago County Emergency Services were alerted to this fire at 0417 UTC. The background temperature for the 3.9 µm imagery on this date was around -16ºC. Pixel brightness temperatures increased to -2.6ºC between 0438 and 0454 UTC.

Thanks to Rich Mamrosh, NWS Green Bay, for alerting us to this interesting case!

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A large and rapidly-deepening midlatitude cyclone (surface analyses) moved northeastward across the Midwest and Great Lakes on 24 February 2019. GOES-16 (GOES-East) Mid-level Water Vapor (6.9 µm) images (above) showed the storm circulation that featured a pronounced dry slot — strong winds were widespread, with gusts of 60 knots or higher occurring in 16 states (WPC storm summary). New February records for lowest pressure were set in northern Michigan at Alpena (978.7 hPa) and Sault Ste. Marie (976.6 hPa). Blizzard conditions closed many interstates and highways across the Upper Midwest.

1-minute Mesoscale Domain Sector GOES-16 “Red” Visible (0.64 µm) images (below) revealed the eastward motion of wind-driven ice across southern Lake Michigan.

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