The National Weather Service (NWS) and NESDIS are implementing a change to the default Mesoscale Domain Sector (MDS) locations for GOES-17. On March 5, at 1500 UTC, MDS #2 will have its default location changed to Alaska, to better serve the Alaska region of the National Weather Service. The image above shows the approximate location of the new default, centered at 56º N, 150º W (versus 35.5º N, 101.5º W). (Link). 

The default location before the switch for MDS #2 is shown in this image from AWIPS.  The toggle below, using SIFT, shows the approximate locations of current and future  default MDS #2.

Mesoscale sectors now and in the near future can be viewed at this site.

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Himawari-8 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) revealed an interesting standing wave west/northwest of Tropical Cyclone Pola in the South Pacific Ocean on 26 February 2019. The long-lived wave first became apparent just before 0800 UTC, and persisted until about 2330 UTC.

The standing wave feature was also apparent in Himawari-8 “Clean” Infrared Window (10.4 µm) images (below). The abrupt warming of cloud-top infrared brightness temperatures associated with the wave suggests that subsidence was lowering the cloud height. Also note the very cold cloud-top temperatures of -90ºC and colder (yellow pixels embedded within the darker purple enhancement) — this was colder than the tropopause temperature on 12 UTC rawinsonde data from both Nadi, Fiji (NFFN) to the southwest and Pago Pago, American Samoa (NSTU) to the northeast (the wave feature was located closer to the Nadi sounding).

Consecutive VIIRS Infrared Window (11.45 µm) images from Suomi NPP and NOAA-20, as viewed using RealEarth (below) showed a definitive bore-like structure with the wave, especially along the northern end.

Himawari-8 “Red” Visible (0.64 µm) images (below) showed the feature during daylight hours — a distinct shadow was being cast during local sunrise, which indicated a sharp drop-off in cloud height from east to west along the wave.

A HWRF-P model sounding for the latitude/longitude point 15.42ºS/179.75ºW valid at 18 UTC (source) showed directional wind shear at the 450 hPa pressure level — such a wind shear could have acted to initiate a horizontal roll circulation, creating a narrow zone of cloud-eroding subsidence. In addition, a sharp change in wind direction was seen above 150 hPa on the Paga Pago sounding — and the Nadi sounding showed speed shear with height — which also could have induced a horizontal roll circulation within the upper troposphere.

An interesting phenomenon was the apparent “shedding” of high-altitude cloud material from the higher/colder cloud canopy of Pola immediately east of the wave feature, as seen in Himawari-8 Shortwave Infrared (3.9 µm) images (below). The westward direction and velocity of this cloud material motion had good agreement with GFS model winds at 150 hPa. Note that this shed cloud material appeared warmer (darker gray) in the 3.9 µm imagery — the shearing of cirrus cloud may have acted to fracture the ice crystals, making them smaller in size and therefore more efficient reflectors of incoming solar radiation.

A toggle between GOES-17 (GOES-West) Infrared and Water Vapor images from the CIMSS Tropical Cyclones site (below) showed that the feature was aligned with a couplet of low-level convergence and upper-level divergence at 15 UTC — such an environment could also support a vertically-propagating gravity wave.

Another analysis of this feature is available from the Australian Bureau of Meteorology Training Centre.

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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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