Mission Summary
20180910H1 Aircraft 42RF [WC06A]
Hurricane Florence (AL06)
Mature Stage Experiment / Ocean Winds

Mission Plan :

NOAA42 will conduct a research mission for the Mature Stage Experiment, as well as for the Ocean Winds Experiment (NESDIS IWRAP instrument). The initial plan calls for a butterfly pattern with 90 nmi legs (Fig. 1), which is oriented with an IP to southwest of the storm. We'll start inbound on the 240°/outbound 60° azimuths, then inbound 360°/outbound 180° azimuths, and finally inbound 120°/outbound 300° azimuths (similar pattern as yesterday's flight).The first leg is timed and oriented for a CYGNSS underpass beginning around 1400 UTC, although our late departure will make that underflight less than ideal. There will be dropsondes at the endpoints, midpoints, and centers in the butterfly, and at the radius of maximum wind (RMW) as dictated by our objectives. AXBT combo drops with dropsondes are anticipated at the midpoints, a couple of the endpoints, as well as at the start of the SFMR High Incidence Angle module (part of the SFMR Experiment, Objective #1), and for IWRAP, if flown later in the mission. Time permitting, following the completion of the butterfly survey pattern, we'll proceed into repeated penetrations in high wind and rain areas for Ocean Winds. Sondes would be required for that module. NHC requested fixes and sondes for every center pass. The P-3 will recover in St. Croix following the science portion of the mission.

Figure 2. GOES-16 IR imagery of Florence from 1120 UTC 10 September [from Tropicaltidbits.com]

Figure 3. GOES-16 visible imagery of Florence from 1120 UTC 10 September [from tropicaltidbits.com]

Hurricane Florence has continued its rapid intensification event that began yesterday, and now has a small eye visible in satellite imagery (IR imagery, Fig. 2, visible imagery, Fig. 3). Overall, the environmental conditions appear to be favorable for continued rapid intensification (shear low, Fig. 4, SSTs high), unless an eyewall replacement cycle occurs. As of the 5 AM NHC advisory, Hurricane Florence is located at 24.9°N/58.9°W, MSLP of 969 hPa, intensity of 90 kt, and moving west-northwest at 8 kt. The 1800 UTC SHIPS (valid towards the end of the mission) is 119°/5 kt (1200 UTC SHIPS is 127°/4 kt. We expect the rapid intensification to conclude during the mission, with a major hurricane heading westward towards the U.S. (Fig. 5).

Figure 4. IR imagery and CIMSS-derived deep-layer (850-200-hPa) vertical wind shear (contoured; contours colored by favorability for intensification, with green being "favorable", yellow being "neutral", and red being "unfavorable"), valid at 0900 UTC 10 September (images courtesy CIMSS, tropic.ssec.wisc.edu)

Figure 5. NHC forecast for Florence from the 5 AM AST forecast advisory on 10 September

Mission Summary :

Figure 6. Actual flight track for mission 20180910H1. Flight-level winds (barbs) and wind speeds (shaded, kt) indicated.

Figure 7. Actual flight track for mission 20180910H1, but does not include the Ocean Winds module after the butterfly. Flight-level winds (barbs) and wind speeds (shaded, kt) indicated. (from Tropicaltidbits.com)

The actual track of the mission is shown in Figs. 6 and 7, with wind information at flight level (FL), extrapolated minimum sea level pressure (MSLP), and SFMR surface wind speed and rain rate shown in Fig. 8. The planned azimuths and timing of the initial pass through the storm did not require any updating at the pre-flight brief as we were delayed enough for the satellite validation to be not as coincident. The takeoff had been delayed an hour due to maintenance on the airplane after the previous day's flight. During our inbound to the IP, Florence certainly continued to show increased symmetry in the CDO within the inner core, suggesting that the precipitation was symmetric (which the Tail Doppler radar [TDR] reflectivity composite from the mission confirms, Fig. 9), and that intensification was likely continuing (TDR analysis confirms a strong, symmetric inner core wind field, as well; Fig. 10).

Figure 8. Time series of flight-level wind speed (green, kt), SFMR surface wind speed (blue, kt), and SFMR rain rate (red, mm/hr) for mission 20180910H1, as well as the extrapolated surface pressure (mb) (bottom, teal, mb) and altitude of the aircraft (bottom, black, m).

As we approached the IP, Jason Dunion also suggested that he was seeing a possible diurnal pulse approaching the radius near our IP in the IR satellite loop. We painted some of that band as we approached our IP on a pseudo downwind approach from the north. After an 1.5 hour transit, we arrived at the IP around 1512 UTC, dropped a sonde (Sonde #1), and went inbound on the 240° azimuth to the center. After a few minutes on the inbound leg we passed through that possible diurnal pulse, but only observed echo tops to about 8 km. There was some embedded convection, but the band was predominantly stratiform precipitation (Fig. 11). We dropped a sonde at the midpoint (Sonde #2) of the leg, and a sonde/AXBT (Airborne expendable bathythermograph) combo release at the radius of maximum wind (RMW) (Sonde #3 / AXBT Combo #1), and proceeded into the eye. We did a "closest approach" (not a fix) of the center at 1535 UTC, with an approximation of the center location near 24°59'N / 60°7'W. The extrapolated pressure from flight altitude was 945 hPa (Fig. 8), and a splash pressure of the center sonde (Sonde #4) of 947 hPa (Fig. 7). On the outbound leg, we released 2 RMW sondes (Sonde #5, #6), with the first being an AXBT combo release (AXBT Combo #2). We also dropped a sonde at the midpoint of the 060° outbound leg (Sonde #7), outside of a rainband. As we went outbound, we had to deviate a little south, and track more eastward to pass through an intense rainband stretching from the southeast to the northeast (Fig. 9) at around 60-80 nmi from the center. Presumably this band could have also had an origin as a diurnal pulse. We experienced quite a bit of turbulence and observed a lot of deep convection in this band (inbound/outbound TDR transect through center and band shown in Fig. 11). After passing through it it's east, we called the endpoint for the radar analysis at 1557 UTC, dropped the sonde (Sonde #8), and turned downwind to head towards our northern point of the butterfly.

Figure 9. Composite reflectivity and winds at (left) 2 km, as well as (right) windspeed at 2 km (shaded) and streamlines at 2 (black) and 5 km (grey)

Figure 10. Composite winds at (left) 0.5 and (right) 2.5 km

On the downwind leg, we were able to fly through a moat region, painting that intense band off to the west of our track, pretty much all the way up from our previous endpoint to the northern point for our next pass. We arrived at the northern point at 1617 UTC (Sonde #9) and went inbound. We dropped the midpoint sonde (Sonde #10) to the south of a rainband we passed through - one of several on the way to the eyewall (Fig. 12). Another sonde was dropped near the RMW (Sonde #11), and we proceeded to fix the center. The second center fix was at 1642 UTC near 25°3'N / 60°19'W. The extrapolated MSLP was 942 hPa (Fig. 8), and the sonde surface pressure was 943 hPa (Sonde #12) (Fig. 7). On the outbound to the south, another RMW sonde was released (Sonde #13), as well as the midpoint sonde as planned (Sonde #14). After about 40 nmi, the conditions below the aircraft were much clearer, with a little less rain coverage (Fig. 12). We arrived at the endpoint around 1702 UTC (Sonde #15) and turned downwind for our final pass of the center for the butterfly pattern.

Figure 11. TDR reflectivity (shaded) and vertical velocity (contoured) cross section from SW to ENE between 1512 and 1556 UTC.

Figure 12. TDR reflectivity (shaded) and vertical velocity (contoured) cross section from N to S between 1617 and 1702 UTC.

As we proceeded downwind to our southeast point, we were painting that intense rainband (perhaps diurnal pulse that we first experienced on the east side on our first outbound pass to the ENE, Fig. 11) with the TDR for much of the downwind leg (Fig. 9, SE quadrant). Given that intense band intersected our IP of our next inbound turn from the SE, we decided to turn inbound early on the 135° azimuth (315° heading), rather than the 120° azimuth, as originally planned. We dropped a sonde at the turnpoint (Sonde #16) when we reached it around 1716 UTC. On the inbound, we again observed less persistent precipitation (in coverage) radially inward of the intense band (Fig. 13). Precipitation picked up again near the midpoint, where we released another sonde (Sonde #17). As we approached the center inbound, an RMW sonde was released with an AXBT (Sonde #18 / AXBT Combo #3). We fixed the center a third time near 25°8'N / 60°31'W (Sonde #19) at around 1736 UTC. The MSLP on this pass was consistent with the previous pass, ~943-944 mb. We proceeded outbound on the 315° azimuth, dropping a final sonde combo at the RMW outbound (Sonde #20 / AXBT Combo #4) and a sonde-only at the midpoint (Sonde #21) on the leg. We arrived at the endpoint of the leg at 1757 UTC (Sonde #22), which completed the butterfly survey pattern. In total, we were able to complete 3 TDR analyses from the butterfly.

Figure 13. TDR reflectivity (shaded) and vertical velocity (contoured) cross section from SE to NW between 1716 and 1757 UTC.

Figure 14. TDR reflectivity (shaded) and vertical velocity (contoured) cross section from NE to S between 1800 and 1840 UTC.

Upon reaching the endpoint to the northwest, we turned inbound to center on the same azimuth. This marked the beginning of the Ocean Winds Module for NESDIS and data collection of their IWRAP instrument. We dropped an RMW sonde inbound on the 305° azimuth (Sonde #23), and fixed the center a fourth time near 25.2°N / 60.6°W at 1818 UTC (center Sonde #24). From there, the outbound was to the south, where we dropped another outbound RMW sonde (Sonde #25). Considering the length of the inbound (305°) and outbound (180°) legs, we were able to generate one final cross-section TDR profile analysis (Fig. 14). From this point until finishing the science portion of the mission, there were a series of repeated legs basically between the S/SW and N/NE quadrants of the storm for the NESDIS Ocean Winds module (Fig. 15). Sondes were dropped inbound/outbound at the RMW on each radial penetration (Sondes #26-43), with a few additional center fixes on passing. Overall the pressure was not observed to drop much more during the flight (Fig. 8). In total, there were 6 additional passes through the center during this module.

Figure 15. Actual flight track for mission 20180910H1, including the Ocean Winds module after the butterfly. Flight-level winds (barbs) and wind speeds (shaded, kt) indicated (from Tropicalatlantic.com).

Mission Evaluation / Problems :

Overall, we were able to observe the conclusion of the rapid intensification (RI) event that had intensified the storm from 70 kt from the previous day's mission, to nearly 125 kt observed during this mission. The MSLP did drop some while we were in storm, from 946 down to about 942 hPa, but that was observed between the first and second passes (note that the first pass was not an official fix, so it could have been lower). NHC issued an updated advisory from 100 kt to 120 kt (969 to 946 mb) after our first pass. The RI event appeared to be ending while we were out there, as the MSLP did not drop much (maybe a couple mb) during the mission. There was some suggestion of a secondary wind maximum in the flight level winds in our passes through the northern quadrants of the storm, but it wasn't a strong signature. This does at least suggest possible development of a secondary eyewall formation (SEF) forthcoming. Early in the mission, we also appeared to sample an intense rainband associated with a diurnal pulse. It wasn't particularly impressive on our first inbound from the SW (mostly stratiform), but was observed to be intense on our outbound to the ENE (even required deviations on our outbound). We should assess later as to whether this was a diurnal pulse and whether the band we sampled to the SW is the same one as we sampled outbound to the ENE, and subsequently to outbound to the south on the second pass through the storm.

We successfully completed the butterfly pattern, with full coverage of dropsondes at the endpoints, midpoints, and center fixes. The AXBTs did not give us any good data, therefore, we won't be measuring the surface fluxes, as intended, at those 4 quadrants RMWs during the butterfly. The NESDIS Ocean Winds measurements from IWRAP were also very successful during this mission, as we did repeated passes through high winds and rain in the eyewalls during an additional 6 passes of the storm center. Four TDR analyses were produced and sent to EMC, 3 from the butterfly, and one additional one on the first of the Ocean Winds Module.

The PIP was still not working during the mission; however the C-band on IWRAP was fixed in time for the mission and collected a very unique dataset.

Jon Zawislak
Oct. 29, 2018

Timeseries wind, SFMR wind, rain rate, altitude and pressure plots

Flight-level wind plot

Flight track	Temperature and Moisture	Wind and Atlitude
Flight track detail

Flight Director's log | Flight Director's manifest | NetCDF data | 1 second data | serial data
LPS log | Radar log | Drop log

---